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SS-265 USS Peto, First Freshwater Built Submarine

Launching of the Peto (Harry Burns, photographer for Manitowoc Shipbuilding Co,

The SS-265 USS Peto was the first United States Gato class submarine built by a freshwater shipyard, the Manitowoc Shipbuilding Company. The shipyard was located on Lake Michigan in the port city of Manitowoc, Wisconsin. It was Manitowoc’s first time building a submarine.   Amazingly, the men and women working on the sub managed to finish 288 days before the date specified in the contract for delivery. They made a total of 28 submarines of the Gato class and Balao class submarines for the war effort.

The USS Peto was laid down on the 18th of June in 1941, months before the infamous attack on Pearl Harbor in December of 1941 (USS PETO (SS 265)). After 10 months of labor, she was launched sideways, in the Great Lakes ship builders’ tradition, into the Manitowoc River. The reason for the sideways launch was constraints, primarily the water depth and width of the river. She was the first submarine ever to be launched sideways. The sponsor, Mrs Emanual A Lofquist, broke the launching Champagne bottle on the bow of USS Peto on April 30, 1942 (USS PETO (SS 265)).

Specifications and Armament

USS Peto on a special dry dock. Photo by Norman Polmar
USS Peto on a special dry dock. Photo by Norman Polmar

The specifications of the Peto were similar to other submarines of the Gato class of fleet submarines: length of 311 feet, 9 inches and a beam of 27 feet, 3 inches. Floating on the surface, the Peto drew slightly more than 15 feet (SS-265). Accommodations aboard the Peto were quite cramped as it has a surface displacement of only 1,526 tons and housed a crew of six officers and 54 enlisted men for patrols up to 75 days in length (SS-265.

Each patrol had varied weapon load outs. The main and stealthy option was located in the hull of the Peto and other Gato class submarines.  The hull was equipped with ten torpedo tubes of 21 inch diameter, in the configuration of six in the bow and four in the stern. The standard torpedo was the Mark 14 which was replaced in later patrols with the electrically driven Mk 18 torpedos. The  two types of “fish” were Peto’s primary offensive weapons of the war, accounting for all but one of her kills. Browning machine guns in .30 and .50 caliber could be mounted depending on the conning tower space or hand held, along with various handheld crew weapons stored in the hull. The first five patrols had a 3 inch/50 caliber dual purpose gun for anti aircraft use and surface action. After the first patrol, the 3”/50 caliber gun was moved forward of the conning tower. The fourth patrol was just after some modifications to the pilot house on the conning tower which allowed the use and installation of a 20 millimeter Oerlikon automatic cannon. The Oerlikon was fed by a 60 cartridge drum magazine making it useful for anti aircraft, small boats and for antipersonnel. This was used frequently to dispose of anti-shipping mines on numerous patrols. The sixth patrol featured a 4 inch/50 caliber deck gun instead of the dual purpose 3”/50; the 4”/50 could not be used against aircraft. The 4”/50 gun was short lived, being replaced for the 7th through 10th patrols with a 5 inch/25 caliber deck gun. A single 40 millimeter Bofors antiaircraft gun was installed on the eighth patrol, which also could be used to attack small surface targets. US Navy gun naming convention names the gun by caliber and the barrel length in multiples of the caliber. The 3”/50 gun would have a barrel length of 3 inches multiplied by 50, meaning 150 inch (12.5 feet) long barrel.

USS Peto in Action

The USS Peto served exclusively in the Pacific theater of World War Two, undergoing 10 combat patrols from bases in Brisbane, Australia and Pearl Harbor. However, she was made in a shipyard on a freshwater river connected to a Great Lake, a way to reach the ocean was needed. This required the sub to be put on a special barge on the Illinois and Mississippi Rivers after commissioning on November 21st, 1942 and then recommissioned after reaching New Orleans around January of 1943.

She left Brisbane on 2nd of April 1943 for her first combat patrol under the command of Lieutenant Commander William T Nelson. The goals were to reconnoiter Greenwich Island, hunt both the Truk-Rabaul shipping lanes and the Pelews-Rabaul shipping lanes.  In the Pellews-Rabaul area, the Peto fired three torpedoes at Japanese shipping, claiming one possible torpedo hit. She returned to port for rearmament and refit on the 20th of May 1943. Overall, the first mission was deemed unsuccessful by naval staff. (“First Patrol”)

The second patrol was again under Lt. Cdr. Nelson in the Truk-Rabaul area from Brisbane. This patrol was from 10th June 1943 to 4th August 1943, lasting a total of 52 days at sea. The Peto fired five torpedoes at enemy vessels, achieving three hits: one naval auxiliary ship sank (2000 tons) and one tanker to limped away damaged (10000 tons). This was Peto’s first successful patrol, as deemed by the naval staff. (“Second Patrol”)

The third patrol left Brisbane 1st September 1943 again under Lt. Cdr. Nelson to patrol the Bismarck Archipelago and Admiralty Islands. She managed to reconnoiter the harbor at Nauru while in the patrol area.  The crew of the Peto fired six torpedoes, sinking two freighters with three torpedo hits for a total of 10500 tons. The Peto also participated in her first attempt at lifeguarding by searching for the crew of a downed 5th Air Force bomber while on patrol. The commanding officer made special notes about the poor quality of the cooks (“Third Patrol”). Usually submarine crews had the best meals for of any service for most of the patrol. After running out of fresh food, K rations would be consumed. A point made during tours on the USS Cobia at the Wisconsin Maritime Museum. This patrol was also part of an ongoing test of voice modulator equipment for use in communication between submarines. The Peto and Scamp had issues communicating at a range of 45 miles however the Peto and Drum had a successful use of the equipment on the same patrol at a range of 150 miles. (“Third Patrol”)

The fourth patrol was the last in the Peto for Lt. Cdr. Nelson, leaving from Brisbane on 14th November 1943 and returning 55 days later on 7th January 1944. The Peto fired 12 torpedoes and managed to only get one hit, sinking a freighter of 8200 tons. One of the misses was from an erratic torpedo run. This was the first patrol with the modified conning tower and the 20mm cannon. (“Fourth Patrol”)

The fifth patrol was commanded by Lt. Cdr Paul Van Leunen Jr leaving Brisbane 25th January 1944. She arrived at Pearl Harbor on 29th March 1944 to acquire a major overhaul instead of the standard 18 day overhaul. The Peto sank a freighter of 4400 tons. One of the major issues was four faulty torpedoes that could not be used due to extremely poor conditions. The patrol area was around New Guinea. The commanding officer complained about contaminated fuel which could have helped cause a fire in the engine room on March 18th; the fire was the main reason for overhaul. (“Fifth Patrol”)

The sixth patrol left Pearl Harbor under the command of Lt. Cdr. Van Leunen Jr on 28th April 1944 and returned 19th June 1944. The sixth patrol marked the first time the Peto was used in a wolf pack with the Picuda and the Perch. The pack was under the leadership of F.W. Fenno in the Picuda. Also this was the first and only patrol with the 4”/50 gun. Also it marked the first patrol with the Mk 18 electric torpedoes. The Peto had an unsuccessful patrol. On 26th May, the Peto ran into some fishing nets and buoys. The crew managed to get the submarine out, but it dragged the buoys and alerted the fishermen. If the buoys remained stuck, the Peto could have easily been found by Japanese sub hunting aircraft and/or destroyers. Stealth is the submarine’s best defense. Later in the patrol, the 20mm was used in an attempt to sink a red buoy.  After arriving at Pearl Harbor, the Peto left for San Francisco for a major overhaul, and then returned to Pearl. (Sixth Patrol”)

The seventh patrol started on 23rd October and returned 6th December 1944, under Lt. Cdr. Robert Caldwell, Jr. leaving from Pearl Harbor to patrol the Yellow Sea. She was joined in a wolf pack by the Sunfish and Spadefish with the Spadefish being the lead ship. This was the first patrol with the 5”/25 deck gun. The Peto sank four ships totaling 28500 tons and damaged a vessel of 4000 tons. (“Seventh Patrol”)

The eighth patrol left Pearl Harbor 31st January 1945 and returned 9th April 1945 to Midway under the command of Lt. Cdr. Caldwell Jr. The strategy was a wolf pack, like the last few missions, with Thresher and Shad. This patrol had a distinct lack of torpedo worthy targets, and the amount of aircraft made gun attacks on the numerous junks unfeasible. The removal of Japans supply lines is proving to work with the lack of torpedo worth targets.  The patrol area was in the South China Sea and the Luzen Strait area. (“Eighth Patrol”)

The ninth patrol left Midway 4th of May 1945 and arrived at Guam 19th of June 1945 under the command of Lt. Cdr. Caldwell Jr. The mission was to perform lifeguard duty for allied airmen and reconnoiter the Kii Suido and Irako Suido Islands. The major complaint about this mission was the lack of information the crew of the Peto was given. For example:the number of planes in a bomber squadron and information on when allied aircraft would be bombing Marcus. On 12th June, the Peto received Lt. Arthur A Burry from the Trutta in rough seas. In an interview with fighter pilot Arthur Burry said the submarines would start by Iwo Jima and head to Japan looking for downed airmen in the water. (“Ninth Patrol”)

The tenth and last patrol of the Peto left Guam on 14th  of July and returned to Pearl Harbor under the command of Lt. Cdr. Caldwell Jr. The mission was lifeguard duty however the Peto got her first and only gun kill on a sampan (50 tons) with 20mm and 40mm cannon fire. The lifeguarding operation was successful, the Peto picked up 12 survivors including one with a gunshot wound which was treated by the crew’s doctor. One of the survivors was from the HMS Formidable. The patrol area was in Tokyo Bay-Nanpo Shoto. The war was finally over. (“Tenth Patrol”)

The Peto was used three ways: alone, wolf pack and lifeguard duty with air cover. A typical solo patrol would cover assigned sectors of the Pacific to the submarine in unrestricted submarine warfare. Wolf packs would be used mid to late war to increase the effectiveness against Japanese shipping. Several submarines would be coordinated to search the same area in close communication. Once a convoy was found, it would be stalked until the available submarines in the area could be assembled to dispatch the convoy. Its a tactic taken from the Germans. Lifeguard duty was simple, patrol at set distances from the airbases and targets so that aircrews could successfully ditch their aircraft and be rescued.   Each mission type did have its successes and its failures, however it shows a strategy shift with US fleet submarine use during the Second World War in the Pacific theater of operations. The mid to late war was similar in style to the German U-boat tactics in the North Atlantic Ocean. Success did improve when working with other vessels and aircraft as seen during the seventh and tenth patrols. The submarines did the job that was needed in the war of attrition with an island nation spread out in the vast Pacific Ocean. So much so, that Japan was forced to use smaller sampans instead of tankers and other merchant vessels. Without inbound material, Japan could not afford to out produce the Allies.

The Peto and her crew sank seven Japanese vessels, and rescued downed airmen while on lifeguard duty during various patrols. This directly contributed to the war effort by sending what the transports were carrying to the bottom of the ocean, thus contributing to a war of attrition. Also, rescuing airmen helped keep experienced airmen alive and back in the fight. In addition to the war of attrition contributions, the USS Peto also served in a role of denying the enemy of shipping lanes, thus forcing the Japanese to send escorts with their transports and/or find new lanes to use. On her 10th and last patrol, the atomic bombs were dropped, ending the war.

After the war the Peto was used in the naval reserve, and then after 1956 used as a training submarine until it was sold for scrap in 1960. The Peto was used in solo and wolfpack roles, supporting the war of attrition against Japan, along with performing search and rescue as part of lifeguard duty for the large air raids against the Japanese cities and manufacturing centers.

Primary Sources:

  1. Nelson, William T. U.S.S Peto: Report of First War Patrol. US Navy, 1943.
  2. Nelson, William T. U.S.S Peto: Report of Second War Patrol. US Navy, 1943.
  3. Nelson, William T. U.S.S Peto: Report of Third War Patrol. US Navy, 1943.
  4. Nelson, William T. U.S.S Peto: Report of War Patrol Number Four. US Navy, 1944.
  5. Van Leunen,Jr. Paul. U.S.S Peto: Report of War Patrol Number Five. US Navy, 1944.
  6. Van Leunen,Jr. Paul. U.S.S Peto: Report of War Patrol Number Six. US Navy, 1944.
  7. Caldwell, Jr, Robert H U.S.S Peto: Report of War Patrol Number Seven. US Navy, 1944.
  8. Caldwell, Jr, Robert H U.S.S Peto: Report of War Patrol Number Eight. US Navy, 1944.
  9. Caldwell, Jr, Robert H U.S.S Peto: Report of War Patrol Number Nine. US Navy, 1945.
  10. Caldwell, Jr, Robert H U.S.S Peto: Report of War Patrol Number Ten. US Navy, 1945.
  11. Burry Interview Arthur Burry 


Secondary Sources:


  1.  “Wisconsin Maritime Website.USS PETO (SS 265).
  2.  Larson and Hestad (2009) Wisconsin Hometown Stories: Manitowoc-Two Rivers minutes 40:32 to 46:00
  3. NavSource Online: Submarine Photo Archive.Submarine Photo Index. Ed. Gary Priolo. Michael Mohl. 
  4. SS-265, U.S.S. Peto – Fleet Submarine.Fleet Submarine
  5. Submarine Warfare of World War II Rare Documentary.YouTube.

Additional Reading:

Gato Class Submarine Tours