Big, Bigger, Biggest: Episode 2

Tuesday 4th August 8.00pm

Continuing this week is the new series of the show that explores major leaps in engineering. The second instalment reveals how six technological breakthroughs enabled the construction of gigantic submarine the USS Pennsylvania.

First commissioned in 1989, the USS Pennsylvania is the biggest submarine in the western world. However, the construction of this mammoth underwater warship would not have been possible without six key innovations…

The first submarine was the Turtle, built during the American war of independence in 1776. American warships were no match for the might of the British navy, so engineers designed a vessel that could carry a bomb underwater. The Turtle was built from two hollowed-out pieces of oak, held together with iron hoops and sealed with tar. Former submarine commander Jonty Powis is stunned when he gets inside the Turtle. “I’ve been in it for two minutes and I already feel like I want to get out,” he says. However, the air in the Turtle lasted for just 25 minutes. The Pennsylvania uses electrolysis to split sea water into air – producing 4,000 litres of oxygen every hour.

Manoeuvrability was the next major leap in submarine technology. During the American civil war in 1864, engineers invented the spa torpedo – a barrel of gunpowder that sat on a spike pole. To deliver the bomb, the submarine had to drive at the same depth as its target. Confederate engineers copied the physiology of a fish by putting metal fins on the side of submarine the HL Hunley. Inside the vessel, the fins were moved up and down using levers. The pressure allowed the captain to control the depth and angle of his attack. The Pennsylvania still uses this technology today by transmitting operators’ instructions electronically to fairwater planes. “We can essentially fly the ship much like an airplane under water,” says captain Bradford S Neff.

Submariners now needed a way of attacking ships from a distance. During the second world war, the Germans developed the U-66 submarine. The first torpedoes were propelled by a tank of compressed air, but they left a tell-tale trail of bubbles. The U-66 carried 22 torpedoes, powered by a batteryoperated electric motor. This arsenal could attack multiple targets and was responsible for sinking 33 ships. Aboard the Pennsylvania, the torpedoes are not limited to firing in a straight line. Optic fibres spooling out of the back of the torpedo carry commands, allowing the weapon to steer toward its target. On-board sensors then guide it in for the kill.

However, the U-66 needed to be refuelled regularly, making it a sitting duck for enemies. Engineers had to find a way of making fuel last longer, and it was provided by the dawn of the atomic age in 1945. American scientists developed the first nuclearpowered submarine, the USS Nautilus, in 1954. A nuclear reactor broke down uranium, triggering a release of heat. Steam shot through turbines, forcing them to rotate at high speed and driving the propellers. “The impact of the Nautilus was tremendous,” says Jonty Powis. “Suddenly you had a submarine that could travel anywhere in the world.”

The development of the Nautilus meant that submarines could stay at sea for longer, but the race was on to build the first submarine with a rocket-powered atomic bomb. Built in 1960, the USS George Washington used a compressed air seal to shoot rockets. Moments before launching, the seal was blown apart and a valve opened, shooting compressed air into a launch tube. Nuclear warheads on this submarine were more powerful than all the bombs dropped in both world wars combined. The George Washington actually prevented war, because the concept of warfare between nations possessing these devastating vessels became unthinkable.

The remaining problem for thePennsylvania was stealth. The ship needed to remain undetected, but the noise produced by the propeller could give its position away. Could engineers develop a quieter propeller with enough thrust?

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