Oh nice! Thanks for the explanation. I love the 120mm Whale! Piercing weapons are great anyhow. Allright, I'm gonna try this next time. See you around! ;)

Hatches can always be damaged, even it's closed.
If you are in the closed hatch, you can damage to it easily.

Furthermore, there is a tiny hitbox in corners of the hatch.
You can shoot it with certain weapons like I listed in my comment.
These weapons, except for Limpet Gun series, have an ability of penetration, or reflection.
Whale means Artillery, 120mm and 150mm cannons.

You can easily reproduce the result by using Limpet Chain Gun ZD or Five Card XB.

How can you damage it while its closed?