All depth charges are shown to explode near enough to the sub to be killing blows. The pressure blasts would rip the sub apart.
These boats would be stacked with supplies. Bread, meat, fruits and tins would be everywhere in sight. In the series the supplies are almost absent.
Whilst (Texas) Holdem form of poker has been around since the early 1900s, it has only been widely popular since the 2000's, it is far far more likely that the sailors would have been playing five-card Draw poker.