Hi Gerard

There were for sure problems with the durability of the Liberty ships, especially in a latter stage when it was tried to reduce the building times even more. In several cases Liberty ships broke in two in heavy weather, in a few cases even in calm seas. But the Liberty ships attacked by U-boats were almost all from the earlier series and proved in many cases difficult to sink. U-510 for example hit six Liberty ships in convoy BT-6 with one torpedo each, but none sank. Of course one has to take in account that in this case the Liberty ships were en route in ballast and not too far from land to be saved.

I made this analysis of U-boat attacks on US Liberty ships. There were 127 ships involved (83 sunk, 23 total loss, 21 damaged)

66 were hit by 1 torpedo (27 sunk, 18 total loss, 21 damaged)
40 were hit by 2 torpedoes (38 sunk, 2 total loss)
15 were hit by 3 torpedoes (13 sunk, 2 total loss)
4 were hit by 4 torpedoes (3 sunk, 1 total loss)
2 were hit by 5 torpedoes (2 sunk)

Not many freighters of this size (around 7000 grt) survived two torpedo hits. I think the Liberty ships were sturdy built and could absorb more damage than other comparable ships, many of them had a long career after the war ended.

Best regards
Rainer

Crew member of uboat.net