1 Sep 1942
The target of an attack by an American Catalina flying boat (Sqdn. VP-73) in the Atlantic in position 58.08N 27.33W, previously credited with sinking U-756, was in fact U-91, which escaped with minor damage.

12 Sep 1942
An escort from convoy ON 127 fired on U-91, causing minor damage. (Sources: Blair, vol 2, page 31.)

21 Feb 1943
While attacking a convoy the boat was hit by a "rain of aircraft bombs and depth charges from surface ships" and forced to give up the attack to repair damage. (Sources: Blair, vol 2, page 186)

27 Mar 1943
22.45 hrs, Bay of Biscay, inbound: a British Wellington bomber (RAF Sqdn 172/M) made a Leigh Light attack. The boat escaped undamaged, but had dived with three men still on the bridge. It resurfaced immediately and found two still in place, but the PO who had fired the AA gun until the last moment was missing. [Oberbootsmaat Heinrich Hollenborg] (Sources: Ritschel)

26 Oct 1943
The target of the depth charge attack on 26 Oct. 1943 in the Atlantic in postion 50.49N 41.01W by a Canadian B-24 Liberator (RCAF Sqdn. 10/A), formerly credited with sinking U-420, was in fact U-91, which escaped unscathed. U-91 was searching for U-584 to supply her with fuel.

31 Oct 1943
Avengers from the USS Card found U-91 refuelling U-584 and called in other aircraft. After initially repelling them with flak, U-91 dived while U-584 stayed on the surface. U-584 was sunk with all hands by Fido homing torpedoes when she attempted to dive. U-91 escaped unscathed and escaped the subsequent search. (Sources: Blair, vol 2, page 438)

6 recorded attacks on this boat.