The submarine was powered by two Germaniawerft F46 four-stroke, six-cylinder supercharged diesel engines producing a total of 2,800 to 3,200 metric horsepower (2,060 to 2,350 kW; 2,760 to 3,160 shp) for use while surfaced, two Siemens-Schuckert GU 343/38–8 double-acting electric motors producing a total of 750 metric horsepower (550 kW; 740 shp) for use while submerged.

A straggler from Convoy HX 227, Wade Hampton was en route to Murmansk from New York, carrying 8,000 tons of general cargo as well as two PT boats (RPT-1 and RPT-3).

[6] After this success, U-405's seventh war patrol began badly, when at 19.24 hours on 4 May 1943, only two days out of Saint-Nazaire, the boat was attacked in the Bay of Biscay by a British Halifax GR.II Series IA bomber of 502 Squadron, RAF Coastal Command.

While returning home, on 18 May, northwest of Cape Finisterre, U-405 was bombed again, this time by an Australian Sunderland patrol bomber of 10 Squadron, although she escaped without any damage.

This was a unique battle: unlike other modern naval actions, it was decided by ramming and small arms fire at extremely close range.

Borie's crew had a limited number of small arms, the German deck mounts were completely open and had no protection.

In the extended and bitter fighting that ensued, dozens of German sailors were killed in desperate attempts to man the 8.8 cm (3.5 in) deck gun.

U-405's tighter turning radius effectively prevented Borie from bringing her superior firepower to bear; Hopman did a masterful job of maneuvering his badly damaged boat with his remaining crew.

The submarine did indeed attempt to speed away, and Borie switched her searchlight back on and turned to bring her guns and a depth charge thrower to bear.

"[8]The survivors were observed firing Very star-shells: Borie's crew believed this to be a distress signal, and maneuvered in an attempt to recover them from their rubber rafts, as they approached to 50-60 yards off the port bow.