Photo courtesy Rosie Darling, sister of MMOM2 Leroy Bleasdell USS Swordfish (SS 193) crew poses on deck, sometime after her 12th wartime patrol. Note the Japanese flags denoting the 21 vessels the sub had sunk in those patrols.

The Swordfish, a 1,450-ton Sargo-class submarine, tested Capt. Karl G. Hensel personally and professionally, said George Billy, chief librarian at the Maritime Marine Academy in Kings Point, N.Y., during a lecture at the Navy Museum May 20.

Hensel, a strict disciplinarian, had been a submarine school instructor before he became a submarine division commander in 1943.

‘‘He was bothered by the fact that he was sending young commanders on patrol he himself had not been on,” said Billy, who is researching the Swordfish for a future book.

The Swordfish conducted its first war patrol the day after the Japanese attack on Pearl Harbor. While patrolling west of the Philippines, the submarine sank four freighters weighing from 3,900 tons to 9,400 tons and damaged a fifth ship. When Hensel took command of the Swordfish on Dec. 17, 1943, the submarine and its crew had destroyed or damaged several Japanese ships throughout the Pacific.

Hensel didn’t get along with the crew during the first 10 days he was in command, said Billy. The submarine’s new commander knew he had to change his attitude if he wanted to retain experienced crew members.

Hensel began asking crewmembers their opinion about whatever concerned the operation of the submarine. He also took them into his confidence without lowering his standards. When Hensel took the Swordfish to sea on Dec. 29, 1943, he had a sufficient number of qualified and experienced personnel aboard.

During the first few days of the 10th war patrol, Hensel and his crew confronted foul weather and two to three inches of water in the control room. These were minor setbacks compared to what the submarine encountered after reaching its patrol area, the entrance to Tokyo Bay, on Jan. 10, 1944.

Thirty-seven minutes after midnight on Jan. 14, Yamakuni Maru, an armed passenger cargo ship was spotted near Tokyo Bay. Hensel ordered the firing of four torpedoes, which sank the Yamakuni Maru. Two days later, the Swordfish sank the Japanese auxiliary gunboat Delhi Maru off Miyake Jima, Honshu, Japan

The Swordfish sank the Japanese auxiliary gunboat Kasagi Maru 130 nautical miles south of Tokyo Bay on Jan. 27. Its 10th war patrol terminated at Pearl Harbor Feb. 7.

‘‘The 10th war patrol was a morale booster for the crew of the Swordfish,” said Billy. ‘‘For Hensel, it was proof that he could be a submarine commander and command a submarine during a war patrol.”

The Swordfish went on two more war patrols from March to June in 1944 under the command of Lt. Cmdr. K.E. Montrose. On her 13th patrol, which began Dec. 26, 1944, the submarine was ordered to also conduct photographic reconnaissance of Okinawa. It was last seen by USS Kete (SS 369) in the Okinawa area on Jan. 12, 1945.

All 89 men aboard the Swordfish were presumed lost at sea, including Billy’s uncle, Motor Machinist 2 Michael Billy.