The most difficult weaponry riddles

Nuclear reactor requires no oxygen for combustion and emits no exhaust gas. It gives the submarine the ability to operate submerged at high speeds, for unlimited periods, dependent only on the endurance of its crew. Nuclear power revolutionized the submarine, finally making it a true "underwater" vessel, rather than a "submersible" craft.

The MXY-7 Navy Suicide Attacker Ohka (pictured) was a manned flying bomb that was usually carried underneath a Mitsubishi G4M2e "Betty" Model 24J bomber to within range of its target; on release, the pilot would first glide towards the target and when close enough he would fire the Ohka's three solid-fuel rockets. The Japanese produced approximately 850 Ohkas, and seven US ships were damaged or sunk by them throughout the war.

Kaitens had a very limited diving depth, which in turn limited the diving depth of the host submarine. This is one of several factors blamed for the very poor survival rate of submarines armed with kaitens: eight submarines being lost for the sinking of only two enemy ships and damaging several others.

The original Siegfried Line (German: Siegfriedstellung) was a First World War line of defensive forts and tank defences built by Germany in northern France during 1916–17 as a section of the Hindenburg Line. In English the term "Siegfried Line" commonly refers to the "Westwall", the German term for a similar Second World War-era defensive line built further east during the 1930s opposite the French Maginot Line.

In the final stages of World War II, the Japanese used Kaitens, manned torpedoes. Early designs allowed the pilot to escape after the final acceleration toward the target, but provision was dropped later. The kaiten could operate for several hours, and it was able to attack several times in case of a miss.

The Shinyo ("Sea Quake") were Japanese suicide boats, driven by one man, to speeds of around 30 kn (56 km/h; 35 mph). Around 6,200 Shinyo were produced for the Imperial Japanese Navy and stored on the coast of Japan for the ultimate defense against the invasion of the Home Islands. Only a small number of them were used in action in the Phillipines and Okinawa, sinking some gunboats and auxiliary ships.