Invincible Jap Merchants?

[RTP2121]

Alright so I'm on patrol heading from Midway, I accomplish my goal of patrolling around wake for 4 days and decide to go hit Tokyo bay up first thing.

Just to get into the bay I have to sink a destroyer, and a rigged tug boat with depth charges. As i proceed up into the shallows I come across a stationary Fuso, which after one lucky hit and several chain explosions she sinks, I also nab another destroyer, two liners (those european titanic looking ones), and a light cruiser as im weaving around from harbor to harbor all around Tokyo. Then I come up to this docked merchant, put two torps in her, one center, one in her stern she starts listing pretty bad but doesn't sink. So i put another torp in her, this time further towards the bow lists even more but still doesn't sink.

Anyways I end up putting 7 torps in this merchant all up and down her starboard and she still doesn't sink, she's listing at least 45 degrees and the waves are cresting at the second "balcony" level of her superstructure and over half her deck is either submerged or has waves crashing on it, she's been on fire for two days (I used time compression to try and see if she would eventually sink) and she's been experiencing chain explosions periodically during that time as well. Yet I still have no credit for sinking her and must now leave my happy hunting grounds to run back to midway or dutch and rearm.

What gives?

[Ships-R-Us]

Is it possible that the merchant that is tied to the dock does not have enough water under her keel to sink as you expect?

[RTP2121]

Ive had ships in shallows before, this ship is not touching the bottom has I'd say maybe 20-30 feet under her still and every other time, even if the ship does not fully submerge i've gotten credit for a kill.

For example one of the destroyers I sank went down stern first and her bow, as well as part of her superstructure and rigging were left protruding out of the water.

Still I was given credit as having sank the destroyer, this merchant however refuses to die.

[Armistead]

The issue is still probably shallow water. I take it you're not using mods and ships ususally sink fairly easy in stock. Damage zones are different. Sometimes it you can't sink em with torps due to shallow water, if you can without getting killed, use your deckgun. If you cause enough damage topside by damage it should sink.

It doe's appear that ships moored to the piers or dock don't sink as easy as those that aren't in the same shallow water. Could be somehow fixed, ect, just don't know, but they often are much harder to sink.

Could also be a bugged ship of which they're several in ports.