TC at 1024 returning port and crashing in some unknown object and destroying sub and crew. Happened more than once.... very dumb. But also leaving port with TC at 8 and sub being destroyed. Found out I kept plotting a course right into Lorient's minefields.
Dumber.
And worst of all... being in a big hurry to install a cool mod only to lose the whole career.... I was at sea.
Dumb was the first time I did that and lost 24 patrols in a very good career. Second time was dumber, but I lost only 14.