Pre-Patrol 1

4 Jun 1942 - 9 June 1942

Patrol 1

12 Jun 1942 - 30 Jul 1942

No sinkings

Patrol 2

28 Aug 1942 - 20 Oct 1942

利根丸 Tone Maru

りすぼん丸 Lisbon Maru

Patrol 3

12 Nov 1942 - 31 Dec 1942

Patrol 4

21 Jan 1943 - 18 Mar 1943

Patrol 5

12 Apr 1943 - 29 May 1943

Patrol 6

19 Jun 1943 - 3 Aug 1943

Patrol 7

25 Aug 1943 - 11 Oct 1943

Patrol 8

1 Mar 1944 - 28 Apr 1944

Patrol 9

22 May 1944 - 6 Jul 1944

Patrol 10

14 Aug 1944 - 15 Oct 1944

Patrol 11

9 Nov 1944 - 1 Jan 1945

Patrol 12

3 Mar 1945 - 26 Apr 1945

Current research credits Grouper with sinking 4 ships totalling 17,983 tons. These figures are the same for Alden-McDonald and JANAC.

SORG credits Grouper with 4 ships and 23,900 tons sunk.

Japanese Naval and Merchant Ship Losses - JANAC on the NHHC website

JANAC on the Hyperwar website - https://www.ibiblio.org/hyperwar/Japan/IJN/JANAC-Losses/JANAC-Losses-6.html

SORG- http://archive.hnsa.org/doc/subreports-sorg.htm (Excel spreadsheet download)

Archives of the Pacific Fleet Submarine Museum (PFSM)

War Patrol Reports - USS Grouper

Monthly Losses of Combatant and Non-Combatant Vessels

太平洋戦争時の喪失船舶明細表（汽船主体）- Lost Vessel table during the Pacific War (merchant vessels)

Alden, John D., and McDonald, Craig R. - U.S. & Allied Sub Successes in the Pacific & Far East during WWII - Fourth Edition, 2009

Cressman, Robert - The Official Chronology of the U.S. Navy in World War II, Naval Institute Press, 2000.

Wrecksite - https://www.wrecksite.eu/wrecksite.aspx

Miramar Ship Index - https://www.miramarshipindex.nz/

Imperial Japanese Navy Page - http://www.combinedfleet.com/

Wikipedia Japan - https://ja.wikipedia.org/wiki/

Japan Center for Asian Historical Records - National Archives of Japan - https://www.jacar.go.jp/index.html

Official U.S. Navy Photos - Naval History & Heritage Command

Archives of the Pacific Fleet Submarine Museum (PFSM)

Imperial Japanese Navy Page - http://www.combinedfleet.com/

Japanese Merchant Ship photos - Wrecksite - copyright owners retain all rights. Photos used on this site will be taken down should the owner request their removal.