1. U-48  (Germany)

 The U-48 was the most feared German submarine in the Atlantic Ocean during World War II. It was in service for only two years and completed 12 patrols (Feindfahrten), but sank an unparalleled 51 targets for a total tonnage of 300,537.

The U-48 shared measurements and features with other Type VIIB vessels (24 total), at 66.5 meters in length, a height of 9.50 meters, a beam of 6.20 meters, and a draft of 4.74 meters. The armament, typical of a Type VIIB U-Boat, included a C30 20 mm anti-aircraft gun and 14 torpedoes fired from five 53.3 cm (21 in) torpedo tubes. Alternatively, the sub carried 26 TMA mines, laid on the bottom in shallow seaways, and detonated when a big ship passed over their position.

While the record is stellar, the U-48's participation in World War II is not without controversy. At the beginning of the war, while sailing near the British coast, the U-boat sank the British merchant ship Royal Sceptre. The U-48's captain, Herbert Schultze, displayed compassion for the defeated vessel's crew when he ensured that they were rescued by another British ship. However, the following year, the U-48 (with a different commanding officer) torpedoed the SS City of Benares, a British steam turbine ocean liner whose passengers included civilian evacuees, many of them women and children, traveling from Britain to Canada. The Allies objected, calling it a "barbaric" attack, while the Germans claimed it was a legitimate military target. To this day, the incident remains a dark stain on the U-48's record.

2. U 99 (Germany)

A Type VIIB German vessel, the U-99 U-Boat, provided service for less than one year in the Kriegsmarine but was successful in sinking 38 enemy ships for a total of 244,658 tons. The submarine's efficiency rate of 38 ships per year was better than that of the U-103, which sank 46 ships over four years.

  The U-99 measured 66.6 meters long (light hull), with a pressure hull of 48.8 meters, a beam of 6.2 meters, and a draft of 4.74 meters. While the outer hull allows water to enter, maintaining equal pressure on both sides for underwater buoyancy, the pressure hull is built with a specific structure made of thick high-strength steel that withstands the outside pressure that increases with diving depth and maintains normal atmospheric pressure inside.

The U-99 traveled at 17.9 knots (33 km/h) on the surface and 8 knots (15 km/h) when submerged. The boat boasted a surface range of 16,095 km and a submerged distance of 175 km. The U-99 was armed with five 53.3 cm (21 in) torpedo tubes, four in the bow and one in the stern. It carried 14 torpedoes or 26 TMA mines and a C30 20 mm anti-aircraft gun.including four battle stars, two Presidential Unit Citations, and the Medal of Honor.

3. USS TAG (USA)

The USS Tang was the most successful American submarine of World War II, measured by the number of ships sunk (33 enemy ships totaling 116,454 tons). It was awarded numerous honors, including four battle stars, two Presidential Unit Citations, and the Medal of Honor.

The USS Tang measured 287 feet long, with a beam of 27 feet 3 inches and a draft of 19 feet. The submarine traveled at a maximum of 20 knots on the surface and 18 knots when submerged. Fairbanks-Morse Type 3 diesel engines with 4500 hp propelled the sub on the surface, and two electric motors with 5600 hp powered two shafts and propellers below the surface. Built with six 21-inch torpedo tubes forward and two 19-inch torpedo tubes aft, the sub carried Mark 37 torpedoes using electrical propulsion and eight Mark-49/57 mines.

4. IJN I -168

Perhaps one of the best-known conflicts of World War II in the Pacific was the Battle of Midway in June 1942, during which four Imperial Japanese Navy aircraft carriers – the Akagi, Kaga, Sōryū, and Hiryū – were sunk. Less well-known is the damage inflicted by Japanese submarines on the U.S. Naval fleet during the battle. The IJN Submarine I-168 sank the carrier USS Yorktown and the destroyer USS Hammann.

Commissioned on July 31, 1934, the I-168 measured 323 feet long with a beam of 27 feet and a draft of 15 feet. The Kaidai-class boat, which hosted 60 sailors, reached a maximum surface speed of 23 knots and a speed of 8.2 knots when submerged. It was armed with six 6x533mm torpedo tubes, four fore and two aft, 14 torpedoes, a 10cm. 50 caliber Type 88 deck gun, and a 13.2mm anti-aircraft machine gun.

During its brief service, the I-168 saw only limited action other than the Midway battle. It began when the Japanese Navy deployed the submarine in November 1941 on a reconnaissance mission in preparation for the attack on Pearl Harbor. A week after the bombing on December 7, 1941, the I-168 remained nearby but was detected and attacked by depth charges on December 13. Damage to battery cells and flooded aft torpedo tubes forced the vessel to take refuge for repairs at Kwajalein in the Marshall Islands. The U.S. Navy finally claimed revenge for the USS Yorktown on July 27, 1943, when the USS Scamp sank the Japanese sub in the Bismarck Sea, near New Hanover Island.

5. USS Racher (SS 269) (USA)

Submarines play a significant role in limiting enemy naval operations. During World War II, U.S. Navy submarines made up only two percent of the ocean-going fleet but were responsible for sinking more than 30 percent of the Japanese Navy vessels. Perhaps most impressively, eight of those ships were aircraft carriers. The American submarine success rate in the Pacific during the war resulted in the loss of nearly five million tons of Japanese merchant marine shipping.

The Gato-class submarines, consisting of 54 submarines first launched in August 1941 with the SS-212, made the most significant contribution during the early years. The fleet was later enhanced with the addition of 122 Balao-class subs boasting a thicker pressure hull for increased operating depth. While the USS Rasher is at the bottom of the list of World War II submarines as one of the least effective, the vessel still has an impressive record. The diesel submarine is credited with sinking 18 ships totaling 99,901 tons during the war.

The Gato-class submarine measured 311 feet long with a beam of 27 feet, 3 inches, and a draft of 16 feet, 10 inches. Diesel engines powered the submarine to 20 knots when surfaced, and electric motors provided power for a maximum velocity of 9 knots when submerged. The Rasher was armed with one 50-caliber gun measuring three, four, or five inches in diameter, six bow and four stern torpedo tubes, and 24 21-inch torpedoes. For its exceptional service during World War II, the USS Rasher was awarded four Presidential Unit Citations for outstanding performance in combat patrols and seven battle stars.