Germany Navy U-Boot Spike Hatchdoor

Hi guys,

Thanks for bringing the excitement of History out of me that I didn’t even know I had!

This is probably just a silly question or pointless, but I was intrigued. I was wondering if you guys would happen to know the reason for why the German Navy had Spikes on the Hatch entrance to their U-boots? Considering they’re usually underwater, or temporarily above water for a short amount of time, what purpose does the spikes serve? Potential invaders, birds perhaps? Or something more specific? Cheers guys!

It might be placed after the war, I’m not sure but I’ve included a video where I saw this below here and included the timestamp:

Mhmmm… Thoughts?