NARRATOR: IN THE BATTLE FOR SUPREMACY AT SEA... FEUER.

TARGET HIT.

IT'S SINKING.

NARRATOR: THE NAZIS WAGE A WAR OF TECHNOLOGY.

MAN: IT WAS ONE OF THE MOST INFLUENTIAL DESIGNS OF A GERMAN WEAPON TECHNOLOGY IN THE SECOND WORLD WAR.

NARRATOR: HITLER ORDERS THE DEVELOPMENT OF SECRET WEAPONS BENEATH THE WAVES.

HITLER: WITH THIS, WE WILL GREATLY UNDERMINE THE ENEMY'S NAVAL TACTICS.

NARRATOR: FAST, SILENT, AND DEADLY.

THERE'S A POTENTIAL FOR HITTING 18 SHIPS INSIDE 20 MINUTES.

NARRATOR: THE NAZIS BUILD GIANT STRUCTURES TO PROTECT THESE TERRIFYING MACHINES.

MAN: IT GOES ON FOR ABOUT A QUARTER OF A MILE THAT WAY.

THE SCALE IS JUST BREATHTAKING.

NARRATOR: THEY'LL REVOLUTIONIZE NAVAL WARFARE FOREVER.

MAN: THE TYPE 21 U-BOAT WAS THE ONE WEAPON THAT COULD HAVE BEEN A REAL GAME CHANGER.

NARRATOR: THIS IS THE STORY OF HITLER'S KILLER SUBS.

THE BIGGEST CONSTRUCTION PROJECTS OF WORLD WAR II, ORDERED BY HITLER TO SECURE WORLD DOMINATION... [SPEAKS GERMAN] NARRATOR: NOW THEY SURVIVE AS DARK REMINDERS OF THE FUHRER'S FANATICAL MILITARY AMBITION.

THESE ARE THE SECRETS... OH, MY GOD.

NARRATOR: OF THE NAZI MEGA WEAPONS.

NARRATOR: SPRING 1945, THE NORTH ATLANTIC.

CRUISER AHEAD.

THERE'S AN ESCORT OF DESTROYERS.

PERISCOPE DEPTH.

WE'LL GO UNDER THE ESCORT.

JA.

NARRATOR: U-BOAT ACE CAPTAIN ADALBERT SCHNEE IS ON PATROL IN GERMANY'S DEADLY TYPE 21 U-BOAT.

I CAN SEE THEM.

THEY'RE ONLY 600 METERS AWAY, AND THEY HAVE NO IDEA THAT WE ARE HERE.

NARRATOR: TODAY THE ONLY SURVIVING EXAMPLE OF HITLER'S UNDERWATER SUPER WEAPON LIES DOCKED IN A PORT IN NORTHERN GERMANY.

MAN: THIS IS THE TYPE 21 U-BOAT, AND SHE IS COMPLETELY UNLIKE ANY SUBMARINE THAT'S COME BEFORE.

SHE'S SHAPED LIKE A BLADE RATHER THAN A BOAT.

SHE'S SLEEK.

SHE'S STREAMLINED.

SHE WAS DESIGNED TO FIGHT UNDERWATER.

SHE WAS A TERRIFYING NEW WEAPON OF WAR.

NARRATOR: NICK BRADBEER, A SPECIALIST IN SUBMARINE ARCHITECTURE, IS EXAMINING THE WEAPON THAT CHANGED THE FACE OF SUBMARINE WARFARE.

BRADBEER: THIS WAS THE REASON FOR THE TYPE 21 GOING TO SEA.

IT'S GOT 20 TORPEDOES IN THIS ROOM READY TO GO.

IT WOULD BE ABSOLUTELY DEVASTATING.

NARRATOR: THE STORY OF HITLER'S SUPER SUBMARINE BEGINS IN 1935.

AFTER THE FIRST WORLD WAR, THE VERSAILLES TREATY BANS GERMANY FROM BUILDING SUBMARINES.

HITLER TEARS UP THE TREATY.

HE IS DETERMINED TO EXPAND HIS ARMED FORCES, INCLUDING BUILDING NEW U-BOATS.

WHEN WAR BREAKS OUT IN 1939, GERMANY'S NAVY, THE KRIEGSMARINE, HAS 57 SUBMARINES, A SMALL BUT DEADLY FLEET.

IN THE 5 MONTHS FROM JUNE TO OCTOBER 1940 ALONE, NAZI U-BOATS SINK 311 ALLIED SHIPS.

BUOYED BY THIS SUCCESS, U-BOAT CHIEF REAR ADMIRAL KARL DOENITZ DEMANDS MORE.

TO DESTROY BRITISH MORALE, WE HAVE TO REDUCE THEIR CONTROL OF THE SEA AND THEREBY CUT THEIR LINES OF COMMUNICATION.

THE VERY LIFE OF THE BRITISH NATION DEPENDS ON THEM.

MAN, VOICE-OVER: U-BOATS ARE ABSOLUTELY KEY TO GERMANY'S CHANCE OF STRANGLING BRITAIN'S OVERSEAS MERCHANT TRADE WHICH IS SO KEY TO ULTIMATELY WINNING THE WAR, AND DOENITZ, ADMIRAL DOENITZ, IS CONSTANTLY LOBBYING THE KRIEGSMARINE, UH, GENERAL STAFF AND SAYING, "PLEASE LET ME BUILD US SOME MORE U-BOATS.

U-BOATS IS THE KEY," AND HE'S ABSOLUTELY RIGHT.

NARRATOR: HITLER NEEDS NO PERSUADING.

HE ORDERS THE IMMEDIATE EXPANSION OF THE U-BOAT BUILDING PROGRAM.

OVER THE NEXT 3 YEARS, THE NAZIS WILL BUILD A FORCE OF OVER 350 U-BOATS.

THEY WILL COVER THE ENTIRE ATLANTIC OCEAN FROM AMERICAN TO THE MEDITERRANEAN AND FROM THE ARCTIC TO THE SOUTH AFRICAN COAST.

THE MAINSTAY OF THE U-BOAT FORCE IS THE TYPE 7.

IT'S SMALL, CHEAP, AND QUICK TO BUILD.

ONE MODEL STANDS OUT AS THE MAIN ATTACK VESSEL.

STANDING ON A REMOTE BEACH ON GERMANY'S BALTIC COAST, IS THE LAST REMAINING EXAMPLE OF THIS FEARSOME PIECE OF NAZI TECHNOLOGY.

THIS IS THE TYPE 7C... AND IT'S ALL ABOUT THIS BOW.

THIS IS DESIGNED MORE LIKE A SHIP.

IT'S DESIGNED TO RUN ON THE SURFACE FOR NEARLY ALL OF ITS LIFE.

THIS--THIS PROW SHAPE MAKES IT FASTER AND MAKES IT RIDE MORE EASILY IN THE WAVES.

NARRATOR: IT WAS ALSO DESIGNED TO FIGHT ON THE SURFACE.

IT WAS ARMED WITH GUNS.

THERE WAS AN 88-MILLIMETER DECK GUN UP FORWARD FOR FIRING AT OTHER SHIPS... AND AN ANTI-AIRCRAFT ARMAMENT UP ON THE FIN.

SO HERE WE HAVE THE BOAT'S PROPELLER SHAFTS.

THERE'S TWO OF THESE, ONE ON EACH SIDE, AND THEY DRIVE THESE PROPELLERS.

NOW, THEY MAY NOT LOOK VERY BIG, BUT THERE'S ENOUGH POWER GOING THROUGH THEM TO DRIVE THE BOAT UP TO 17 KNOTS.

NARRATOR: THE TYPE 7C's SPEED ON THE SURFACE IS UP TO 8 KNOTS FASTER THAN MANY ALLIED SHIPS.

IT CAN EASILY OUTMANEUVER THE MERCHANT CONVOYS...

BUT WHAT MAKES THE TYPE 7C SO DEADLY LIES DEEP WITHIN ITS BOW.

AHA.

RIGHT.

WELL, THIS IS THE FORWARD TORPEDO ROOM.

THIS IS ONE OF THE TORPEDOES-- THE G7E.

THERE WERE 8 OF THESE THINGS STORED IN THIS ROOM, UH, AND THEY--THEY WEIGH A TON AND A HALF.

IT'S A HUGE WEIGHT TO SHIFT AROUND, UH, AND TO RELOAD IT, TO GET IT LINED UP TO GO INTO ONE OF THESE TUBES, YOU'D HAVE 10, 12 PEOPLE JUST HAVING TO HAUL THIS THING UP JUST BY HAND AND BY MECHANICAL ADVANTAGE.

NARRATOR: THE TYPE 7C CARRIES 14 TORPEDOES.

ONCE THE CAPTAIN'S DECIDED WHAT HE'S GONNA SHOOT THE TORPEDO AT, HE'S GOT TO PASS THE INSTRUCTIONS FOR HOW DEEP HE WANTS IT TO RUN, HOW FAST HE WANTS IT TO RUN, AND WHAT ANGLE.

[SPEAKS GERMAN] A SAILOR CAN USE THIS DEVICE TO PROGRAM THE TORPEDO'S GUIDANCE SYSTEM FROM HERE, AND THEN AGAIN, WHEN THE CAPTAIN WANTS TO TAKE THE SHOT, THAT CAN'T BE DONE CENTRALLY FROM THE CONTROL ROOM.

IT'S A MANUAL RELEASE.

SOMEONE HAS TO COME STAND HERE, SAFETY OFF, AND THEN FIRE.

AND FINALLY, RIGHT HERE AT THE BACK END OF THE BOAT, SHE'S GOT A STING IN THE TAIL.

THIS IS A FIFTH TORPEDO TUBE POINTING BACKWARDS, SO ONCE SHE'S DISCHARGED HER FORWARD 4 IN AN ATTACK ON A CONVOY, IF SHE HAS AN ESCORT CHASING HER DOWN OR IF SHE'S MAYBE FIRED HER FIRST 4 AND THEN TURNED AWAY TO MAKE A FIFTH ATTACK, SHE CAN FIRE A FIFTH TORPEDO FROM THIS TUBE.

NARRATOR: U-BOAT CAPTAINS LIKE ADALBERT SCHNEE ATTACK MOSTLY AT NIGHT, WHEN A SURFACED U-BOAT IS BARELY VISIBLE.

TARGET SET.

GET READY.

[SPEAKING GERMAN] [SPEAKING GERMAN] SHOOT!

[WHOOSH] [SHOUTING IN GERMAN] NARRATOR: IF THEY'RE SPOTTED, THEY CAN QUICKLY DISAPPEAR BACK BENEATH THE WAVES.

DIVE!

NARRATOR: EARLY IN THE WAR, THE TYPE 7s HAVE INCREDIBLE SUCCESSES, BUT ADMIRAL DOENITZ HAS EVEN GREATER PLANS-- TO UTILIZE ADVANCED TECHNOLOGY TO DESTROY THE ALLIES AT SEA.

IN EARLY 1941, A SECRET NAZI WEAPONS PROGRAM IS DEVELOPING A NEW U-BOAT, ONE WITH THE POTENTIAL TO INFLICT SERIOUS LOSSES ON ALLIED SHIPPING.

IT'S THE BRAIN CHILD OF DR. HELLMUTH WALTER, A PIONEERING GERMAN ENGINEER.

HOLLAND: HELLMUTH WALTER IS A GENIUS-- THERE'S NO QUESTION ABOUT THAT WHATSOEVER-- AND THE GERMANS ARE VERY GOOD AT RECOGNIZING THAT AND REWARDING THAT.

NARRATOR: WALTER HAS BEEN DEVELOPING ROCKET PROPULSION UNITS FOR USE IN BOTH SUBMARINES AND AIRCRAFT SINCE 1934.

HIS MOST FAMOUS CONSTRUCTION IS THE ROCKET MOTOR THAT POWERS THE MESSERSCHMITT ME 163 AIRCRAFT.

THE ENGINE IS POWERED BY WALTER'S SECRET WEAPON, A SUPER FUEL HE'S CREATED USING THE VOLATILE CHEMICAL HYDROGEN PEROXIDE.

IN A U-BOAT, THIS FUEL HAS THE CAPABILITY TO DRIVE IT FASTER AND ALLOW IT TO STAY SUBMERGED FOR LONGER.

BRADBEER: A SUBMARINE THAT USES DIESEL ENGINES HAS TO BE ON THE SURFACE IN ORDER TO RUN THOSE ENGINES.

A PEROXIDE-POWERED SUBMARINE CAN RUN ITS ENGINES AT FULL POWER AT WHATEVER DEPTH IT LIKES.

NARRATOR: DOENITZ SECURES FUNDS FOR WALTER TO DEVELOP A PRACTICAL VESSEL TO TEST HIS SUBMARINE IDEAS.

THE EXPERIMENTAL CRAFT IS CODE-NAMED THE V80.

WALTER DESIGNS A HULL THE SHAPE OF A FIGURE 8.

THE LOWER SECTION IS USED TO STORE THE HYDROGEN PEROXIDE FUEL.

THE UPPER SECTION HOUSES THE ENGINES AND CREW.

TO IMPROVE THE V80's PERFORMANCE UNDERWATER, WALTER ALSO DESIGNS A STREAMLINED OUTER HULL WITH NO EXTERNAL WEAPONS TO REDUCE DRAG.

BRADBEER: IT HAD A NEW SHAPE FOR SUBMARINES, A SHAPE WHICH WAS DESCRIBED AT THE TIME AS MORE FISHLIKE THAN SHIPLIKE.

NARRATOR: IN INITIAL TRIALS, THE VESSEL REACHES UNDERWATER SPEEDS OF 23 KNOTS, 3 TIMES FASTER THAN THE TYPE 7.

BY NOVEMBER 1941, WALTER IS READY TO DEMONSTRATE THE V80 TO HIS PAYMASTERS IN NAVAL HIGH COMMAND.

MEASURING JUST OVER 72 FEET IN LENGTH, THIS SMALL BOAT NOW REACHES THE INCREDIBLE SPEED OF 28 KNOTS SUBMERGED.

[APPLAUSE] DOENITZ RECOGNIZES THE POTENTIAL.

HE RECOMMENDS NAVAL HIGH COMMAND FULLY SUPPORT WALTER AND HIS GROUNDBREAKING WORK.

BRADBEER: THE V80 WAS A HUGE BREAKTHROUGH IN PROPULSION TECHNOLOGY, BUT IT WAS FAR TOO SMALL TO BE A COMBAT U-BOAT.

IT DIDN'T HAVE THE RANGE.

IT COULDN'T CARRY THE WEAPONS.

NARRATOR: WALTER STARTS MODIFYING THE DESIGN.

HE WILL TAKE THE BEST OF THE V80 AND TURN IT INTO A WEAPON OF WAR.

MEANWHILE, DOENITZ HAS A PLAN TO MAKE HIS EXISTING FLEET EVEN MORE DEADLY.

FOR THE FIRST YEAR OF THE WAR, U-BOATS HUNT ALONE, BUT IN 1940 AFTER THE FALL OF FRANCE, THE NAZIS ESTABLISH NAVAL BASES ON THE COUNTRY'S WEST COAST AND USE HIGH-TECH RADIO COMMUNICATIONS TO IMPLEMENT A DEVASTATING STRATEGY.

THE SUBS WILL ATTACK ALLIED CONVOYS IN LARGE GROUPS KNOWN AS WOLFPACKS.

HOLLAND: THE POINT OF THE WOLFPACK IS TO GET AS MANY U-BOATS AS YOU POSSIBLY CAN TOGETHER WORKING IN COORDINATION WITH ONE ANOTHER FOR MAXIMUM EFFECT ON THAT CONVOY OF, SAY, APPROXIMATELY 40 MERCHANT VESSELS.

YOU'RE GONNA HIT MORE AND DESTROY MORE IF THERE'S, SAY, 7 U-BOATS WORKING TOGETHER THAN IF THERE'S JUST ONE.

NARRATOR: DOENITZ KNOWS TIGHTLY CONTROLLED WOLFPACKS WILL GENERATE MAXIMUM DESTRUCTION.

[RADIO STATIC] FOR THESE TO WORK EFFECTIVELY, HE NEEDS A DEDICATED COMMUNICATIONS CENTER TO COORDINATE ATTACKS.

IN 1940, THE NAZIS TAKE OVER A CHATEAU IN THE FRENCH COUNTRYSIDE.

IT'S THE PERFECT BASE FROM WHICH TO DIRECT U-BOAT TACTICS.

HISTORIAN JAMES HOLLAND IS EXPLORING THE SECRETS OF REAR ADMIRAL DOENITZ'S U-BOAT NERVE CENTER.

HOLLAND: IT'S A REALLY RATHER LOVELY CHATEAU, BUT IT SORT OF REMINDS ME A LITTLE BIT OF THOSE FIRST WORLD WAR GENERALS IN THEIR CHATEAU HQs.

ON THE OTHER HAND, I SUPPOSE HE WAS THE HEAD OF THE GERMAN NAVY, SO YOU WOULDN'T REALLY EXPECT HIM TO SLUM IT.

CHATEAU DE PIGNEROLLE IS STRATEGICALLY LOCATED BETWEEN PARIS AND ALL OF THE MAIN COASTAL U-BOAT BASES.

ITS CONTROL HUB LIES IN A NETWORK OF STRUCTURES THAT THE NAZIS ADDED.

THIS IS GOING UNDERNEATH THE GARDEN OF THE CHATEAU.

IT'S SOME 400 FEET LONG, ABOUT A 120 YARDS OR SOMETHING LIKE THAT.

I'VE BEEN TOLD THERE'S 3 FOOT OF CONCRETE ABOVE THIS AND THEN A FURTHER 3 FOOT OF SOIL, SO, UH, THE ROOF OF THIS IS ABOUT 6 FOOT UNDER THE--UNDER THE GARDEN.

OH, LOOK.

I CAN SEE AN ARROW PAINTED ON THE WALL HERE, FLUORESCENT, PAINTED ON BY THE GERMANS, AND HERE'S ANOTHER ONE... AND YOU CAN SEE HERE A--A VENTILATION SHAFT.

OH, LOOK.

IT EVEN OPENS, SO THIS WOULD HAVE BEEN ABLE TO CONTROL THE FLOW OF AIR DOWN HERE.

WOULD NEED IT.

NARRATOR: THE TUNNEL LEADS UP A STAIRWAY TO A SEPARATE BUNKER COMPLEX ON THE SURFACE.

THIS NERVE CENTER RELAYED ORDERS BETWEEN NAVAL HIGH COMMAND IN BERLIN AND THE U-BOATS.

WHAT I'M LOOKING FOR IS THE MAIN BIG ROOM, THE MAIN COMMUNICATIONS ROOM.

WHAT'S DOWN HERE?

I THINK I'VE FOUND IT.

I THINK THIS MUST BE IT.

THIS IS WHERE THE SIGNALS COME FROM THE U-BOATS TO HERE AND BACK OUT AGAIN TO SEA, AND IT'S AMAZING TO THINK THAT BACK IN THE WAR, THIS WOULD HAVE JUST BEEN A HIVE OF ACTIVITY.

YOU'D HAVE HAD LOTS OF DESKS ALONG THE WALLS AND PEOPLE WITH TELEXES AND--AND ENIGMA MACHINES.

PEOPLE WOULD HAVE BEEN WORKING HERE ON SHIFTS 24/7.

I MEAN, THEY'RE HERE ALL THE TIME.

U-BOATS DON'T GO TO SLEEP.

THEY'RE--THEY'RE WORKING OUT IN THE OCEANS.

THERE'S NO WINDOWS, OF COURSE.

THERE'S NO NATURAL LIGHT.

LOOK AT THAT ROOF.

THAT'S THE ORIGINAL CORRUGATED CEILING.

IT'S GOT A KIND OF NEW FALSE CEILING PUT IN-- THAT WAS WHEN THE FRENCH ARMY USED IT AFTER THE WAR-- BECAUSE IT WAS GOOD ENOUGH TO BE A NUCLEAR BUNKER.

THE REASON IT'S GOOD ENOUGH TO BE A NUCLEAR BUNKER IS BECAUSE THERE'S 11 FEET OF CONCRETE ABOVE THIS.

NARRATOR: THE COMPLEX IS COMPRISED OF 11 BOMBPROOF BUNKERS BUILT TO PROTECT OVER 1,000 COMMUNICATION STAFF WHO MAINTAINED CONSTANT CONTACT WITH DOENITZ'S U-BOAT FLEET.

IT FEELS SOLID.

YOU KNOW, YOU'D FEEL SAFE DOWN HERE.

I KEEP SAYING, "DOWN HERE", BUT, OF COURSE, YOU'RE NOT.

YOU'RE ACTUALLY ABOVE GROUND, BUT IT FEELS LIKE YOU'RE IN THE DEPTHS OF THE EARTH, BUT--BUT, IN ACTUAL FACT, THIS IS ABOVE GROUND LEVEL.

LOOK AT THIS DOOR HERE.

IT'S BIG AND METAL AND SOLID AND GASPROOF, AND I'VE BEEN TOLD THAT THESE WEIGHED AS MUCH AS A TON EACH.

WONDER IF I CAN OPEN IT.

OH, IT MOVES.

NARRATOR: THE ONLY VISIBLE CLUE TO WHAT HAPPENED HERE WOULD HAVE BEEN ROOFTOP RADIO MASTS.

HERE'S ANOTHER BUNKER AND DEEP IN THE TREES IN THE WOODS OF THE GROUNDS, AND THIS BUNKER HERE IS ALMOST BURIED UP TO ITS ROOF, BUT HERE'S A LADDER.

THIS PARTICULAR BUNKER HAD LOADS AND LOADS OF ANTENNAE.

NARRATOR: MESSAGES SENT VIA THE SHORTWAVE RADIO ANTENNA COULD TRAVEL THOUSANDS OF MILES TO U-BOATS ON THE OTHER SIDE OF THE ATLANTIC.

YOU CAN SEE HERE, THIS ONE'S JUST BEEN HACKED OFF, NOTHING LEFT, BUT IN THE WAR, THEY WOULD HAVE BEEN, WELL, AS HIGH AS THESE TREES, SOME SORT OF 40 FOOT HIGH.

NARRATOR: UNDER DOENITZ'S COMMAND, IN THE FIRST TWO YEARS OF THE WAR, U-BOAT SUCCESSES STEADILY INCREASED.

GERMANY IS ON THE BRINK OF STARVING BRITAIN INTO SUBMISSION.

IN 1941, NAZI U-BOATS SINK 501 SHIPS.

U-BOAT ACES LIKE CAPTAIN SCHNEE ARE THE SHARPSHOOTERS OF THE SEA.

THE CONVOY IS HOLDING COURSE, DISTANCE-- 1 KILOMETER.

GOOD.

ALL IN POSITION?

IN POSITION.

NARRATOR: USING STEALTH TACTICS TO STUN THE ENEMY, EVEN THE ORDER TO FIRE IS ISSUED WITH A WHISPER.

TARGET SET.

TUBE ONE READY?

TUBE ONE READY.

TUBE ONE, GO.

TUBE ONE, GO.

TUBE TWO, FIRE.

TWO TUBE, GO.

[WHOOSH] TARGET HIT.

IT'S SINKING.

NARRATOR: THE U-BOATS HAVE THE UPPER HAND, BUT THEN ALLIED MILITARY AND TECHNOLOGICAL ADVANCES REDRESS THE BALANCE OF POWER IN THE ATLANTIC.

THE ALLIES MANAGED TO MINIATURIZE RADAR EQUIPMENT ENOUGH TO MOUNT IT IN AIRCRAFT, AND THIS IS TERRIBLE FOR THE U-BOATS.

AIRBORNE RADAR ALLOWS AIRCRAFT TO SPOT U-BOATS FAR OUTSIDE THE RANGE AT WHICH THE AIRCRAFT ITSELF CAN BE SEEN, AND THEN THE U-BOAT IS ATTACKED WITHOUT WARNING.

NARRATOR: AND, HAVING OCCUPIED ICELAND, THE ALLIES HAVE ANOTHER KEY ADVANTAGE.

HOLLAND: UNFORTUNATELY FOR THE U-BOAT CREWS, THAT'S A STRATEGIC BASE THAT THE ALLIES CAN USE WITH AIRFIELDS, WHICH SUDDENLY MEANS THAT THE NORTHERN PART OF THE ATLANTIC, THAT'S COVERED BY AIRCRAFT, AND AIRCRAFT CAN THEN SWEEP OVER THAT STRETCH OF THE ATLANTIC LOOKING AND SPOTTING FOR U-BOATS.

NARRATOR: NOW THE ALLIES CAN GET A FIX ON U-BOAT POSITIONS.

THE HUNTERS BECOME THE HUNTED... AND IN SPRING 1942, CAPTAIN SCHNEE DISCOVERS JUST HOW VULNERABLE HIS U-BOAT IS WHEN IT SURFACES OFF THE EAST COAST OF THE UNITED STATES.

[KLAXON SOUNDING] WHERE THE HELL DID THAT COME FROM?

CLOSE THE HATCH.

PREPARE TO DIVE.

CLOSE THE HATCH.

DIVE!

THEY KNOW HOW TO FIND US.

THEY KNOW WHERE WE ARE.

NARRATOR: SCHNEE'S U-BOAT ESCAPES, BUT NAZI LOSSES INCREASE.

WORSE, GERMANY CANNOT BUILD U-BOATS QUICKLY ENOUGH TO REPLACE THE LOST VESSELS.

MAN: TO BUILD THESE U-BOATS WAS ABOUT HALF A YEAR THEY NEEDED TO PRODUCE ONE U-BOAT AND ANOTHER HALF A YEAR TO TRAIN THE CREW TO MAKE THEM COMBAT READY.

ANOTHER LIMITING FACTOR WAS, OF COURSE, DOCKYARD CAPACITY BECAUSE YOU NEEDED THE DOCKYARDS ALSO TO--TO MAINTAIN THE REST OF THE FLEET.

HITLER: TELL ME, WHAT'S THE STATE OF THE SUBMARINE WAR?

BECAUSE OF ALLIED AIR COVER, WE ARE BEING PUSHED OUT INTO THE ATLANTIC OCEAN.

THAT SEVERELY REDUCES OUR STRIKE RATE.

WHAT ABOUT OUR LOSSES?

IN THE BAY OF BISCAY, WE ARE INCURRING EVER-GROWING LOSSES THROUGH AIR ATTACKS.

WE NEED TO OUTRUN THEM AND NOT BE SEEN.

NARRATOR: IN 1943, THE GERMAN NAVY LOSES A RECORD 244 U-BOATS AND OVER 10,000 MEN.

THE U-BOAT FORCE IS FAILING...

BUT DOENITZ AND HITLER ARE DETERMINED TO WIN BACK THE INITIATIVE WITH A PLAN THAT WILL REVOLUTIONIZE SUBMARINE WARFARE FOREVER.

FIRST, THEY NEED MORE TRAINED CREW.

GENTLEMEN, WE MUST ALSO PLAN FOR THE LONG TERM.

WITHOUT AN EXPERIENCED U-BOAT FLEET, WE WILL SUFFER LOSSES.

WE NEED EXPERIENCED CAPTAINS WHO TRAIN UP OUR CREWS OF TOMORROW WHO ARE FAMILIAR WITH THE NEW TECHNOLOGIES WE ARE DEVELOPING, MEN LIKE CAPTAIN SCHNEE.

NARRATOR: U-BOAT ACE ADALBERT SCHNEE IS ONE OF THE MEN DOENITZ TASKS WITH LEADING HIS NEW STRATEGY.

REASSIGNED TO U-BOAT HEADQUARTERS IN PARIS, SCHNEE IS RESPONSIBLE FOR ORGANIZING OPERATIONS AGAINST ALLIED CONVOYS, BUT TO REGAIN THE UPPER HAND, HE NEEDS NEW TECHNOLOGY.

CAN YOU BRING ME FILE 93 PLEASE?

EXCELLENT.

THANK YOU.

NARRATOR: THE TYPE 7 IS NOW OUTDATED AND OUTGUNNED.

BRADBEER: IT'S NOT VERY STREAMLINED.

YOU CAN SEE ALL OF THESE FEATURES HERE-- THE BIG SADDLE TANKS FOR THE DIESEL FUEL, THE HANDRAILS AROUND THE BRIDGE, THE ANTI-AIRCRAFT GUNS, EVEN THE VENTS TO DRAIN THE CASING OF FLOOD WATER.

ALL OF THESE JUST ADDED TO DRAG WHEN IT WAS UNDERWATER.

THE WATER RUNNING PAST THEM SLOWED THE BOAT DOWN, AND THAT MEANT THE TYPE 7 COULDN'T BE VERY FAST UNDERWATER, BUT WORSE, AS WELL AS SLOWING THE BOAT DOWN, THESE FEATURES ALL CREATED NOISE.

WATER FLOWING OVER THEM CREATED TURBULENCE, AND THAT INCREASED THE BOAT'S SIGNATURE, MADE IT EASIER TO HEAR ON SONAR.

NARRATOR: ADDED TO THIS, THE TYPE 7's TWO DIESEL ENGINES NEED AIR TO RUN, SO THEY'RE ONLY USED WHEN THE SHIP IS ON THE SURFACE.

WHEN SUBMERGED, THE TYPE 7 MUST USE AN ALTERNATIVE POWER SOURCE, AND ITS SPEED IS MUCH SLOWER.

BRADBEER: WHEN SHE'S SUBMERGED, THROUGH HERE, WE'VE GOT THE ELECTRICAL CONTROL PANELS AND THESE TWO ELECTRIC MOTORS, ONE ON EACH SIDE, ONE FOR EACH SHAFT.

NOW, THESE DRAW POWER FROM THE BATTERIES AND DRIVE THE BOAT WHEN SHE'S UNDERWATER.

THEY CAN'T GO NEARLY AS FAST-- ONLY 5 OR 6, MAYBE 7 KNOTS-- AND THERE'S NOT THAT MUCH POWER IN THE BATTERIES.

NARRATOR: WHEN THEY RUN DOWN, THE BOAT IS FORCED TO THE SURFACE TO POWER UP THE DIESEL ENGINES THAT RECHARGE THE BATTERIES...

THEY KEEP THEIR SPEED DOWN TO 4 KNOTS, THEY CAN STAY DOWN FOR MAYBE A DAY.

IF THEY REALLY EKE IT DOWN TO TWO KNOTS, BARELY WALKING PACE, THEY COULD EKE IT OUT TO TWO, MAYBE 3 DAYS, BUT THAT'S THE LIMIT OF THEIR ENDURANCE.

NARRATOR: BUT ADMIRAL DOENITZ HAS A SOLUTION-- THE ROCKET-POWERED SUBMARINE TECHNOLOGY OF ENGINEERING GENIUS HELLMUTH WALTER.

TO REGAIN THE INITIATIVE AGAINST THE ALLIES, ADMIRAL DOENITZ IS PLANNING A NEW BREED OF SUBMARINE.

WE HAVE A SOLUTION.

THERE IS A SUCCESSFUL DRAFT FOR A NEW SUBMARINE WITH GREATLY INCREASED UNDERWATER SPEEDS.

THIS WILL MAKE THE ENEMY U-BOAT CHASERS ENTIRELY INEFFECTUAL.

IF THAT WAS THE CASE, IT COULD BE REVOLUTIONARY.

MAY I SUGGEST WE DEVELOP THIS NEW TYPE OF SUBMARINE AS QUICKLY AS POSSIBLE?

I'M BACKING YOU COMPLETELY.

WITH THIS, WE WILL GREATLY UNDERMINE THE ENEMY'S NAVAL TACTICS.

NARRATOR: WALTER HAS THE GREEN LIGHT TO BUILD A LARGER COMBAT BOAT BASED ON HIS OLD V80-- HE CALLS IT THE TYPE 18-- BUT ONCE CONSTRUCTION BEGINS, ISSUES ARISE.

ONE OF THE GREATEST PROBLEMS IS WITH THE VESSEL'S HIGH-TECH HYDROGEN PEROXIDE FUEL.

A FLEET OF TYPE 18s WOULD HAVE REQUIRED A HUGE AMOUNT OF HYDROGEN PEROXIDE TO FUEL THEM, AN AMOUNT WHICH GERMANY JUST COULD NOT PRODUCE.

NARRATOR: WITH NO GUARANTEED FUEL SUPPLY PLUS A PROBLEM WITH TURBINE CONSTRUCTION, THE PROJECT IS SHELVED.

DESPITE THIS SETBACK, WALTER'S MAIN CONCEPT WILL NOT DIE.

HOLLAND: THE PRINCIPLES BEHIND IT, THIS IDEA THAT YOU COULD CREATE A SUBMARINE THAT IS TRULY A SUBMARINE AND NOT A SUBMERSIBLE THAT CAN ACTUALLY OPERATE FASTER UNDER THE WATER THAN IT CAN ON THE SURFACE, THAT IS WHAT IS TRULY REVOLUTIONARY.

NARRATOR: U-BOAT ENGINEERS FRIEDRICH SCHURER AND KLAUS BROKING TAKE WALTER'S TYPE 18 DESIGN A STEP FURTHER... WITH THE TYPE 21.

THE IDEA IS TO MAINTAIN WALTER'S REVOLUTIONARY, STREAMLINED, FIGURE-8 HULL DESIGN FOR THE NEW CRAFT.

ELECTRIC AND DIESEL ENGINES DRIVE THE SUB BUT WITH AN ADDED TWIST.

IN THE HULL'S LOWER SECTION SIT MASSIVE BATTERIES 3 TIMES THE SIZE OF THOSE IN THE TYPE 7.

THE TYPE 21 WILL MEASURE OVER 251 FEET IN LENGTH AND 21 FEET IN WIDTH.

IT'S MORE THAN TWICE THE SIZE OF THE TYPE 7C.

WHEN COULD YOU COMPLETE THESE?

NOT BEFORE NOVEMBER, WHICH IS TOO LATE.

SO WE HAVE A CONSTRUCTION PLAN.

THE PROBLEM NOW IS HOW TO EXECUTE IT.

THAT'S RIGHT.

[CROWD CHEERING] NARRATOR: HITLER GIVES THE NEW VESSEL PRIORITY OVER ALL OTHER SUBMARINE CONSTRUCTION.

NAVAL HIGH COMMAND SET A TARGET FOR 15 SUBMARINES TO BE COMPLETED EACH MONTH...

BUT DOENITZ DEMANDS MORE.

HE'S DETERMINED THAT THEY BUILD THE SUBS QUICKER.

IN JULY 1943, HE AGREES TO THE APPOINTMENT OF A SPECIALIST ENGINEER TO MANAGE THE CONSTRUCTION.

I AM AWARE THAT HE HASN'T WORKED ON SOMETHING LIKE THIS BEFORE, BUT I DON'T THINK THAT MATTERS.

HE UNDERSTANDS MASS PRODUCTION.

THAT'S THE KEY HERE.

NARRATOR: HIS NAME IS OTTO MERKER.

HE'S HAD GREAT SUCCESS IN MASS-PRODUCING CARS AND FIRE TRUCKS AND BELIEVES HE CAN BUILD THE TYPE 21 IN THE SAME WAY.

HIS IDEA IS TO MAKE IT IN 3 STAGES.

FIRST, THE MAIN SHELL OF THE U-BOAT IS BUILT IN 9 SEPARATE SECTIONS, BUT TO PROTECT THESE HULL SECTIONS FROM ALLIED AIR ATTACK, MERKER SPREADS THEIR MANUFACTURE ACROSS 32 FACTORIES THROUGHOUT GERMANY.

THESE ARE LOCATED CLOSE TO WATERWAYS TO PROVIDE TRANSPORTATION FOR THE HUGE SECTIONS.

ONCE COMPLETED, MERKER SENDS THE SECTIONS TO 11 DIFFERENT FITTING OUT YARDS FOR STAGE TWO OF THE BUILD-- THE INSTALLATION OF GEARING, ELECTRIC MOTORS, AND SPECIALIZED SUBMARINE EQUIPMENT.

IN BREMEN, THE REMAINS OF SUBMARINE PENS SERVICING ONE OF THESE FITTING OUT YARDS STILL EXIST.

THIS REALLY IS A MONSTER STRUCTURE, AND THIS IS WHERE THE PLANNED PHASE TWO OF THE MASS PRODUCTION OF THE MARK 21 U-BOAT WOULD HAVE TAKEN PLACE.

NARRATOR: JAMES HOLLAND IS VISITING HORNISSE BUNKER.

HOLLAND: THE IDEA IS THAT THOSE HOLLOW BITS OF HULL, THOSE SECTIONS OF HULL THAT HAVE BEEN MADE WITHIN GERMANY, HAVE BEEN SHIPPED UP HERE ON A BARGE, BROUGHT IN HERE, AND HERE, THE SKILLED WORKERS FILL THEM UP WITH THE FIXTURES AND FITTINGS, ALL THOSE COMPONENTS, PUT THEM BACK ON A BARGE, AND OUT THEY GO FOR THE FINAL ASSEMBLY.

NARRATOR: MERKER THEN SENDS THE COMPLETED PARTS TO ONE OF 3 YARDS LOCATED IN DANZIG, HAMBURG, AND BREMEN, WHERE THE 9 SECTIONS ARE WELDED TOGETHER.

DESPITE THIS INGENIOUS PLAN, MERKER CALCULATES THE PROCESS WILL TAKE UP TO 9 MONTHS.

FOR THE NAZIS, IT COULD BE TOO LATE.

TO SPEED UP TYPE 21 PRODUCTION, MERKER ORDERS AN ADDITIONAL CONSTRUCTION FACILITY, ONE CAPABLE OF HOUSING AN ENTIRE PRODUCTION LINE.

BUILT TO WITHSTAND ALLIED BOMBS, IT WILL BE THE ULTIMATE U-BOAT FACTORY.

COMMISSIONED IN 1943, VALENTIN BUNKER SITS BY THE RIVER WESER NEAR BREMEN.

IT'S THE LARGEST BUNKER BUILT BY THE NAZIS IN GERMANY.

THIS WHOLE STRUCTURE, IT GOES ON FOR ABOUT A QUARTER OF A MILE THAT WAY.

THE SCALE IS JUST BREATHTAKING.

NARRATOR: ITS WALLS ARE 23 FEET THICK, AND THE ROOF IS UP TO 15 FEET THICK.

JAMES HOLLAND HAS COME TO EXPLORE INSIDE THIS CONCRETE MONSTER.

I CAN HONESTLY SAY I'VE NEVER SEEN ANYTHING QUITE SO LARGE.

THE SCALE OF THIS PLACE IS TRULY, TRULY ENORMOUS.

ONE CAN ONLY IMAGINE HOW SOMETHING OF THIS SIZE COULD POSSIBLY BE BUILT IN JUST 22 MONTHS.

NARRATOR: AS HITLER LOSES HIS GRIP ON THE WAR, HE GIVES ABSOLUTE PRIORITY TO VALENTIN.

MATERIALS AND RESOURCES POUR IN.

SLAVE LABORERS, MOSTLY CONCENTRATION CAMP PRISONERS AND POWs, ARE USED TO BUILD IT.

THEY WORK LONG SHIFTS WITH ONLY SHORT BREAKS AND LITTLE FOOD.

MANY DIE OF HUNGER, ACCIDENTS, VIOLENCE, AND ARBITRARY KILLINGS COMMITTED BY THE GUARDS.

WORKERS ARE CONSIDERED DISPOSABLE.

THOSE WHO DIE ARE QUICKLY REPLACED.

IT'S DEPRESSING IN HERE.

IT'S GRIM AND FORBIDDING.

YOU CAN'T HELP THINKING ABOUT THE 8,000 WORKERS HERE AND THE 1,600 THAT LOST THEIR LIVES.

THAT'S 4 A DAY, YOU KNOW, SLAVE LABORERS GROUND INTO THE DUST.

NARRATOR: MERKER DIVIDES THIS MASSIVE STRUCTURE INTO 13 SEPARATE BAYS.

EACH ONE WILL CARRY OUT ONE PART OF THE ASSEMBLY PROCESS.

BAYS 12 AND 13 ARE WATERTIGHT AND CAN BE FLOODED FOR UNDERWATER TESTS.

ONCE COMPLETE, TYPE 21s WILL LAUNCH INTO THE RIVER WESER.

THIS IS JUST TWO PARTS.

THIS IS SECTIONS 12 AND 13.

IT'S--IT'S ALMOST BEYOND COMPREHENSION.

WHAT WOULD HAVE HAPPENED IS, THE FINISHED ASSEMBLED U-BOAT WOULD HAVE COME IN HERE ON RAILS, ONTO THIS PLATFORM HERE, AND THEN THEY WOULD HAVE SEALED OFF BOTH THESE COMPARTMENTS AND FILLED IT UP WITH WATER, AND THEN THE U-BOAT WOULD HAVE MOVED INTO THAT SIDE, INTO THE WATER, AND SAILED OUT INTO-- INTO THE RIVER WESER.

NARRATOR: AND THIS IS THE FINISHED PRODUCT, A NAZI MEGA WEAPON UNLIKE ANYTHING THAT HAS GONE BEFORE-- THE TYPE 21.

BRADBEER: HERE ON THE UPPER DECK, IT'S REALLY OBVIOUS HOW CLEAN EVERYTHING IS.

UM, THE STREAMLINING IS REALLY APPARENT.

WE CAN SEE THE CLEAN LINES DOWN THE SIDE, AND THESE BOLLARDS ARE REALLY THE ONLY SIGNIFICANT OBSTRUCTIONS ON THE UPPER DECK.

WHEN THE BOAT WENT TO SEA, THESE WOULD BE DROPPED DOWN UNDER THE CASING SO THE DECK WOULD BE, UH, FLUSH AND SMOOTH AND SIMILARLY WITH THESE-- THESE HANDRAILS.

THEY'RE REALLY IMPORTANT WHILE WE'RE WALKING AROUND ON THE UPPER DECK, BUT THESE COULD BE DISMOUNTED AND TAKEN DOWN BELOW.

WE'RE COMING UP TO THE FRONT NOW, THE BOW OF THE UPPER DECK.

IT'S NOT A BOAT-SHAPED BOW LIKE PREVIOUS SUBMARINES HAD.

IT JUST COMES TO THIS SORT OF ROUNDED, UM, FORWARD END, AND WE'VE GOT HERE, UM-- THESE ARE THE FORWARD HYDROPLANES.

THESE--THESE ARE USED TO CONTROL THE BOAT'S DEPTH, AND AT HIGH SPEED, THEY CAN BE FOLDED AWAY FLUSH INTO THESE SLOTS HERE.

NARRATOR: ALTHOUGH SHE'S MUCH BIGGER THAN THE TYPE 7, AMAZINGLY, THE STREAMLINED HULL PRODUCES A SMALLER ACOUSTIC SIGNATURE, MAKING IT HARDER FOR ENEMY SONAR TO DETECT HER, BUT IT'S THE TECHNOLOGY HOUSED WITHIN THIS FUTURISTIC CASING THAT MAKES THE TYPE 21 REVOLUTIONARY.

SO THIS IS THE POWERHOUSE OF THE SUBMARINE.

THIS IS AN ABSOLUTELY MASSIVE ELECTRIC MOTOR.

NARRATOR: 5,000 HORSEPOWER DRIVES THE PROPELLERS, ENOUGH TO ACHIEVE 17 KNOTS SUBMERGED.

THE TYPE 7 CAN ONLY DO 6 OR 7 KNOTS UNDERWATER, SO THIS IS 2 1/2 TIMES AS FAST.

IT'S A HUGE STEP FORWARD, AND--AND THAT'S REALLY WHAT ALLOWS THE TYPE 21 TO FIGHT UNDERWATER.

UH!

AHA.

SO THESE ARE BATTERIES.

THIS IS REALLY WHAT MAKES THE 21 THE 21.

236 TONS OF BATTERIES FILL THE LOWER HULL, ENOUGH TO POWER THE BOAT FOR 11 DAYS.

THIS IS A PRETTY BIG SPACE, UM, AND THIS IS ONLY ONE SIDE OF IT.

THERE'S A--THERE'S A WHOLE OTHER SIDE THROUGH THERE, AND THEN THERE'S ANOTHER LEVEL DOWN BELOW.

THESE ARE BASICALLY JUST GIANT CAR BATTERIES, UNFORTUNATELY MEANS, WHILE THEY STORE LOADS OF ENERGY, THEY NEED LOADS OF REGULAR MAINTENANCE WHILE THEY'RE IN USE.

NOW, THERE'S A NARROW PASSAGEWAY HERE BETWEEN THE TWO BATTERY TANKS, UM, AND SOME POOR SAILOR WOULD HAVE TO COME DOWN THIS PASSAGEWAY, CLIMB UP THROUGH ONE OF THESE HOLES, AND LIE ON THIS BOARD, AND THEN, UH, HE'D BE ABLE TO SCOOT HIMSELF, UM, BACKWARDS AND FORWARDS BECAUSE THIS THING RUNS ON RAILS, BUT WHILE HE WAS DOING THAT IN THIS CRAMPED SPACE, HE HAD TO BE REALLY CAREFUL NOT TO TOUCH THESE EXPOSED, LIVE ELECTRICAL CONNECTORS.

THERE'S MORE THAN ENOUGH ENERGY IN THIS BATTERY TO KILL YOU.

NARRATOR: THE TYPE 21's TWO DIESEL ENGINES CAN RECHARGE THE BATTERIES WITHIN JUST 5 HOURS.

THEY REQUIRE AIR TO RUN, SO ARE ONLY USED ON THE SURFACE OR AT PERISCOPE DEPTH, THANKS TO THE SNORKEL.

THIS NEW INVENTION ALLOWS AIR TO ENTER THE SUB WHEN JUST BELOW THE SURFACE...

BUT THE TYPE 21's SNORKEL IS INGENIOUS.

IT HAS A BALL VALVE TO STOP WATER ENTERING THE BOAT, AND IT PROVIDES AN INDIRECT AIR FEED TO THE ENGINE.

THE CLEVER THING THAT WALTER DID WITH THIS DESIGN WAS, THE INLET PIPES DON'T DIRECTLY CONNECT TO THE DIESEL.

AIR CAN COME IN DOWN THESE PIPES, AND IT COMES OUT HERE, DIRECTLY ABOVE THE ENGINE'S AIR FILTER.

THE PIPES FEED AIR INTO THE BOAT ITSELF, AND THE DIESEL DRAWS AIR FROM THE ATMOSPHERE OF THE BOAT.

THAT MEANS IF A WAVE GOES ACROSS THE TOP OF THE SNORKEL MAST AND THE VALVE CLOSES, THEN THE DIESELS CAN KEEP RUNNING FOR A LITTLE WHILE BY JUST USING UP THE AIR IN THE BOAT.

NARRATOR: IT MEANS THAT, UNLIKE THE TYPE 7, THE TYPE 21 ENGINES CAN REMAIN RUNNING UNDERWATER, EVEN IN THE ROUGHEST SEA, BUT SPENDING PROLONGED PERIODS UNDERWATER CREATES ANOTHER PROBLEM-- AIR QUALITY.

NOW, ROUND HERE, WE HAVE SOMETHING WHICH IS REALLY EXCITING AND NEW FOR THIS SUBMARINE.

THE TYPE 21 WAS DESIGNED TO STAY SUBMERGED FOR LONG PERIODS OF TIME, AND WITH ABOUT 50 PEOPLE BREATHING, THE CARBON DIOXIDE ON THE BOAT WOULD SLOWLY BUILD UP, EVENTUALLY TO DANGEROUS LEVELS, SO THIS MACHINERY WAS INSTALLED TO ABSORB CARBON DIOXIDE FROM THE AIR.

THESE CANISTERS WOULD BE FULL OF SODA LIME, UH, AND AIR FROM THE BOAT WOULD BE PUMPED THROUGH THEM, AND THE SODA LIME WOULD ABSORB CARBON DIOXIDE FROM THE AIR, AND THE CARBON DIOXIDE LEVEL COULD BE MEASURED AND KEPT WITHIN SAFE LIMITS, SO THIS WAS A NEW TECHNOLOGY, AND THIS IS A TECHNOLOGY WHICH IS STILL IN USE TODAY IN SUBMARINES.

NARRATOR: IN 1944, THIS IS THE MOST SOPHISTICATED SUBMARINE IN THE WORLD.

BRADBEER: ONE THING THAT REALLY STRIKES ME ABOUT THIS BOAT IS THE SHEER COMPLEXITY OF IT.

I HAVE NO IDEA WHAT ALL THESE VALVES DO.

IT'S OVERWHELMING, UM, AND--AND IN A SUBMARINE, EVERY MEMBER OF THE CREW HAS TO KNOW WHAT EACH OF THESE VALVES DO.

EVEN IF THEY DON'T WORK IN THIS SPACE, THEY HAVE TO KNOW THE WHOLE BOAT SO IF THERE'S AN EMERGENCY, THEY KNOW WHICH--WHICH ONE TO RUN TO--TO AND OPERATE, SO TRAINING SUBMARINE CREW IS A REALLY TIME-CONSUMING PROCESS.

AHA.

THIS IS WHAT I WAS LOOKING FOR.

THIS IS A WELD LINE THAT RUNS UP HERE, AND THAT'S--THAT'S THE JOINT BETWEEN WHERE TWO OF THE SECTIONS THE BOAT WAS MADE IN MEET.

NARRATOR: THE 21's INNOVATIVE CONSTRUCTION AND GROUNDBREAKING TECHNOLOGY HAVE ONLY ONE REAL PURPOSE.

IT'S ALL ABOUT HER FIREPOWER.

THIS IS THE BUSINESS END OF THE TYPE 21.

THIS IS ITS MAIN WEAPONS SYSTEM.

WE'VE GOT 6 21-INCH TORPEDO TUBES, UM, THERE'S A PAIR UP HERE, A PAIR DOWN HERE AND ANOTHER PAIR BELOW THE FLOOR.

NOW, EACH OF THESE CAN BE LOADED WITH A TORPEDO, AND THIS IS A REALLY HEFTY WEAPON, AND IT'S GOT ABOUT A QUARTER OF A TON OF EXPLOSIVE IN THE FRONT END.

THAT'S A HUGE WARHEAD.

THESE ARE REALLY ONE SHOT, SHIP-KILLING WEAPONS... AND THE TYPE 21 CARRIES 20 OF THEM-- UM, 6 PRE-LOADED IN THE TUBES AND ANOTHER 14 IN THE TORPEDO ROOM BEHIND IT-- SO WHILE THE TYPE 21 HAD--HAD MORE TORPEDO TUBES THAN THE TYPE 7, THE REAL ADVANCE WAS ITS AUTOMATIC RELOADING SYSTEM.

IT COULD RELOAD ALL 6 OF ITS TORPEDO TUBES IN LESS TIME THAN THE TYPE 7 COULD HAVE RELOADED A SINGLE TUBE.

THIS SUBMARINE COULD HAVE FIRED 18 TORPEDOES INTO A CONVOY IN 18 MINUTES.

IT HAD THE POTENTIAL TO BE ABSOLUTELY DEVASTATING.

NARRATOR: THE TYPE 21 IS QUIETER AND DEEPER-DIVING THAN ANY SUBMARINE THAT HAS COME BEFORE, AND IT'S FASTER SUBMERGED THAN MOST MERCHANT CONVOYS TRAVELING ON THE SURFACE.

THE SUBMARINE IS A LETHAL WEAPON, ONE THAT HITLER'S BEEN WAITING FOR.

AT DANZIG, THE FIRST TYPE 21 IS RUSHED THROUGH CONSTRUCTION TO BE LAUNCHED A DAY BEFORE HITLER'S BIRTHDAY ON THE APRIL 19, 1944.

U3501 IS GIVEN A SPECIAL PRESENTATION TO NAVAL HIGH COMMAND...

BUT IT'S A DISASTER.

THE BOAT IS UNFINISHED.

IT ISN'T WATERTIGHT AND NEEDS BUOYANCY BAGS TO KEEP IT AFLOAT.

FINALLY, THE FIRST COMPETED TYPE 21 ENTERS SERVICE ON JUNE 28, 1944...

ALMOST A YEAR AFTER THE PROJECT'S COMMISSIONING, BUT WATER GETS INTO THE ELECTRIC MOTOR.

SHE RETURNS IMMEDIATELY TO DRY DOCK.

OTHER BOATS ENCOUNTER SIMILAR DIFFICULTIES.

THE COMPLEXITY OF DESIGN AND CONSTRUCTION CREATES TEETHING PROBLEMS, BUT THAT'S NOT THE ONLY ISSUE.

THERE'S STILL A SHORTAGE OF TRAINED SUBMARINERS, AND THE NAVY'S TRAINING PROGRAM CANNOT KEEP PACE WITH DEMAND.

BRADBEER: IT'S IMPORTANT TO TEST NEW SHIPS AS THEY ENTER SERVICE.

UM, IT'S IMPORTANT TO TAKE, UH, AN EXPERIENCED CREW OUT IN A NEW SUBMARINE AND UNDERSTAND WHAT IT CAN DO, WHAT ITS LIMITATIONS ARE.

TO MAKE MATTERS WORSE, THE ALLIES STEP UP THEIR BOMBING CAMPAIGN, TARGETING NAZI HEAVY INDUSTRY.

IT MEANS STEEL IS IN SHORT SUPPLY.

WITT: THERE WAS ALSO THE ARMY CRYING FOR GUNS, FOR SMALL ARMS FOR TANKS, FOR ALL KINDS OF EQUIPMENT, UH, THE AIR FORCE CRYING FOR AIRPLANES AND THE LIKE.

IT WAS TRYING TO HAVE A VERY SMALL CAKE AND TRYING TO FEED AN ABUNDANCE OF--OF-- OF HUNGRY MOUTHS FROM IT.

NARRATOR: ALLIED AIRCRAFT PROWL THE COASTLINE, MAKING ANY TESTING OF THE NEW SUBMARINE IMPOSSIBLE.

THEY BOMB HAMBURG HEAVILY, DESTROYING 3 TYPE 21s IN THE HARBOR... AND THEN TURN THEIR ATTENTION TO THE NAZI'S BIGGEST U-BOAT CONSTRUCTION FACILITY.

IN MARCH 1945, ALLIED AIRCRAFT DROP THEIR BOMBS ON VALENTIN BUNKER.

EVIDENCE OF THESE ATTACKS LITTERS THE ASSEMBLY BAYS.

GOODNESS, LOOK AT THAT.

THAT'S ABSOLUTELY AMAZING.

THAT MUST HAVE BEEN WHERE ONE OF THE TWO GRAND SLAMS THAT WAS-- HIT THE ROOF AND PENETRATED THROUGH, STRUCK, AND LOOK AT ALL THE DEBRIS AROUND, AND--OH, MY GOODNESS-- WHAT'S THIS?

HA!

THIS MUST BE THE LAST REMAINS OF THE GRAND SLAM.

THIS IS A--A 10-TON BOMB.

THIS IS THE BIGGEST THING THE RAF CAN CARRY, DESIGNED BY BARNES WALLIS, WHO, OF COURSE, DESIGNED THE BOUNCING BOMB, AND LOOK AT THE THICKNESS OF IT.

[CLANG] OH, THAT'S HEAVY.

THAT'S JUST A FRACTION OF IT.

I MEAN, I CAN BARELY LIFT THAT UP.

THIS IS CALLED AN EARTHQUAKE BOMB.

THE IDEA IS--IS THAT THE WEIGHT OF IT, THE FORCE OF IT, HITS THE ROOF, PENETRATES THROUGH A HUGE AMOUNT, AND THEN THERE'S A DELAYED FUSE, AND THEN IT EXPLODES, SO IT GOES THROUGH ABOUT 10 OF THE 15 FEET OF THE THICKNESS OF THAT ROOF, THEN EXPLODES, AND THAT'S WHAT DOES FOR IT.

THAT'S WHAT CAUSES THIS, AND WITH THE TWO BOMBS, THERE'S A 1,000 TONS OF CONCRETE COMES DOWN, AND, REALLY, FOR THE VALENTIN ASSEMBLY PLANT, THAT'S IT.

[EXPLOSIONS] NARRATOR: DOENITZ'S ULTIMATE U-BOAT FACTORY IS FINISHED BEFORE IT EVEN BEGINS PRODUCTION.

IT'S A DEVASTATING SETBACK.

THE 3 REMAINING ASSEMBLY YARDS ARE NOW UNDER INCREASED PRESSURE TO GET TYPE 21s OFF THE PRODUCTION LINE.

BETWEEN JUNE 1944 AND APRIL 1945, 119 TYPE 21s ARE DELIVERED IN FULL WORKING ORDER...

BUT DUE TO LENGTHY CREW TRAINING, ONLY TWO GO INTO ACTIVE SERVICE.

DOENITZ PLACES ONE UNDER THE COMMAND OF U-BOAT ACE ADALBERT SCHNEE.

[SONAR PINGS] AFTER TWO MONTHS' GETTING TO KNOW HIS NEW VESSEL, HE'S NOW IN CHARGE OF THE MOST ADVANCED SUBMARINE IN THE WORLD.

ON APRIL 30, 1945, SCHNEE GUIDES HIS CRAFT SILENTLY OUT OF A NORWEGIAN FJORD HEADING FOR THE ATLANTIC OCEAN.

THE FOLLOWING DAY, SCHNEE'S TYPE 21 IS SPOTTED.

WE'VE PICKED UP 4 SUBMARINE CHASERS.

THEY'RE ONTO US.

CHANGE COURSE.

NEW COURSE--TWO-TWO-ZERO, FULL SPEED AHEAD.

NARRATOR: SCHNEE KNOWS HIS TYPE 21 CAN REACH 17 KNOTS UNDERWATER.

NOW THEY HAVE TO FIGHT AGAINST THE WIND.

ARE THEY STILL PICKING US UP?

MAN: NO.

THEY'VE LOST US.

GOOD.

NARRATOR: HE'S BACK ON PATROL, SEEKING OUT ENEMY SHIPPING...

BUT BACK IN GERMANY, THE WAR HAS FINALLY CAUGHT UP WITH DOENITZ AND HIS SUBMARINE FLEET.

THE RED ARMY HAS TAKEN BERLIN, AND HITLER IS DEAD.

ON MAY 4, 1945, DOENITZ MAKES A RADIO BROADCAST TO HIS U-BOATS... DOENITZ: MEN OF THE U-BOAT FORCE, AFTER A HEROIC FIGHT WHICH KNOWS NO COMPARISON IN HISTORY, YOU HAVE PUT DOWN YOUR WEAPONS.

YOU HAVE ACHIEVED THINGS WHICH ARE UNHEARD OF.

THE GREATEST SACRIFICE FOR YOUR FATHERLAND YOU ARE YET TO MAKE.

NO SHADOW WILL BE CAST ON YOUR HONOR, BUT YOUR FATHERLAND WILL BE SPARED THE WORST CONSEQUENCES.

NARRATOR: BUT SCHNEE HAS ONE LAST CHANCE TO DEMONSTRATE THE CAPABILITIES OF THIS TECHNOLOGICAL MARVEL.

HEADING BACK TO NORWAY, HE PICKS UP THE SOUND OF A PROPELLER.

IT'S FROM THE BRITISH DESTROYER HMS NORFOLK.

CRUISER AHEAD WITH AN ESCORT OF DESTROYERS.

WE'LL GO UNDER THE ESCORT.

PERISCOPE DEPTH.

YES.

GOOD.

NARRATOR: SCHNEE LINES UP THE NORFOLK IN THE CROSSHAIRS OF THE PERISCOPE.

I CAN SEE THEM.

THEY'RE ONLY 600 METERS AWAY... NARRATOR: SUBMERGED AND SILENT, THE U2511 IS ALMOST INVISIBLE.

AND THEY HAVE NO IDEA THAT WE ARE HERE.

NARRATOR: IT'S A TEMPTING MOMENT...

BUT THE CEASEFIRE HAS BEEN CALLED.

SCHNEE CHOOSES NOT TO DISOBEY ORDERS.

THAT'S IT.

THE WAR IS OVER.

BRING THE BOAT UP.

WE'RE GOING BACK HOME.

IN GERMANY, ADMIRAL DOENITZ ORDERS U-BOAT DESIGNER HELLMUTH WALTER TO DESTROY ALL EVIDENCE OF THEIR TECHNOLOGICAL MASTERPIECE.

WALTER SPENDS 4 DAYS BURNING 50,000 TECHNICAL CHARTS AND DRAWINGS IN THE GROUNDS OF HIS FACTORY.

THE MAN WHOSE IDEAS SPAWNED SO MANY NAZI MACHINES OF TERROR IS NOW FORCED TO DESTROY HIS WORK.

DOENITZ GIVES ORDERS TO SCUTTLE ANY COMPLETED TYPE 21s TO PREVENT THEM FALLING INTO ENEMY HANDS.

84 ARE DESTROYED, BUT IT'S NOT ENOUGH.

THE ALLIES GET THEIR HANDS ON THE TYPE 21.

IT BECOMES THE MODEL FOR THE WORLD'S FIRST NUCLEAR-POWERED SUB-- THE USS NAUTILUS.

WITT: IN THIS REGARD, IT WAS CERTAINLY ONE OF THE MOST SUCCESSFUL AND INFLUENTIAL DESIGNS OF A GERMAN WEAPON TECHNOLOGY IN THE SECOND WORLD WAR.

NARRATOR: IN A BITTER IRONY, THE NAZIS HAD CREATED THE MOST ADVANCED UNDERWATER SUPER WEAPON IN HISTORY, BUT IT ARRIVED TOO LATE TO SAVE GERMANY AND NEVER EVEN FIRED A SINGLE TORPEDO AT THE ENEMY.

BRADBEER: IF THE TYPE 21 HAD ENTERED THE BATTLE OF THE ATLANTIC TWO YEARS EARLIER IN 1943, IT'S DIFFICULT TO IMAGINE HOW THE ALLIES COULD HAVE MAINTAINED CONVOYS ACROSS THE ATLANTIC-- THERE WAS NO TECHNOLOGY THAT COULD FIND AND DESTROY IT-- BUT THE TYPE 21 ENTERED THE WAR JUST TOO LATE TO MAKE A DIFFERENCE.

POST WAR, ADMIRAL DOENITZ SERVED A 10-YEAR PRISON SENTENCE.

AFTER HIS RELEASE, HE WROTE HIS MEMOIRS AND THEN SANK INTO RELATIVE OBSCURITY.

CAPTAIN SCHNEE SERVED 6 MONTHS IN A NAVAL MINESWEEPER UNIT BEFORE REINVENTING HIMSELF AS A SALESMAN, AN IGNOMINIOUS END FOR TWO GIANTS OF THE NAZI'S U-BOAT BATTLE OF THE ATLANTIC.