I found a list on how to unlock them
Battlestations: Pacific Unlockable: Vehicles
Win the following missions on any difficulty to unlock additional vehicles:
US Campaign
* Allen M. Sumner Class Destroyer - Win Battle of Santa Cruz
* Anti-Submarine Warfare Fletcher Class Destroyer - Win Battle of Cape England
* Atlanta Class Anti-Aircraft Cruiser - Win Battle of Cape Esperance
* B-29 SuperFortress Heavy Bomber - Win Air Raid Aginst Indochina
* Gato Class Attack Submarine - Win Defense of Henderson Airfield
* Iowa Class Battleship - Earn a gold medal on 1st Battle of Guadalcanal
IJN Campaign
* Ahizuki Class Destroyer - Beat "Saving the Shoho"
* Betty with Ohka - Acheive a Gold Medal on "Invasion of Hawaii"
* H8K Emily - Beat "Destruction of Z Force"
* I-400 Carrier Submarine - Beat "Hunt for the USA Hornet"
* J7W Shinden - Beat "Invading of Port Moresby"
* Shimakazi Class Destroyer - Beat "Solomons Skirmish"
* Tone Class Cruiser - Beat "Battle of Java Sea"
* Type B with Kaiten Torpedoes - Beat "Attack on Sydney's Harbour"
* Yamato Class Battleship - Get a Gold Medal on "Invasion of Midway"
Japanese Campaign
* Akizuki Class Anti-air Destroyer - Get a Silver Medal on "Saving the Shoho"
* H8K Emily Flying Boat - Get a Silver Medal on "Destruction of Z force"
* I-400 Submarine - Get a Silver Medal at "Hunt for the USA Hornet"
* J7W Shinden Fighter Plane - Get a Silver Medal on "Invading of Port Moresby"
* Ohka Suicide Rocket Plane (JC) - Get a Gold Medal at "Invasion of Hawaii"
* Shimikazi Advanced Torpedo Destroyer - Get a Silver Medal at "Solomon's Skirmish"
* Tone Class Heavy Cruiser - Get a Silver Medal on "Battle of Java Sea"
* Type B Submarine Equipped (Kaiten equipped) - Get a Silver Medal at "Attack on Sydney's Harbour"
* Yamato Class Battleship - Get a Gold Medal at "Invasion of Midway"
But no, I couldn't find a mod/cheat to unlock them all, but I would apreciate a lot if someone could reveal them, IF they could find it.
Just read the BS:P mods thread, there is a link and information on both mods and methods of unlocking everything.
Also, the IJN Campaign -is- the Japanese campaign, IJN means Imperial Japanese Navy