The new Amphibious Ships- Available at level 150
This isn't as complicated as it seems.
The easiest way to get the ships is to recycle your armed submarine that you got doing Diamond Missions.
You will need an unarmed sub to begin (Buy&Sell>>Vehicles). So when you are ready to Assemble and Arm AAS (Ship), buy as many unarmed subs as you need to complete the process. You don't have to recycle all your subs if you don't want to, you can continously recycle the same sub over and over. The Ship is the better vehicle and the armed sub has no upkeep so it is up to you. For this demonstration, we will be recycling the same sub.
Under Missions>>Recycle
You will do the top missions: Disassemble SCB-304 . This disarms your sub giving you two things: 3 x Raw Materials needed to assemble your ship and one missile needed to rearm your sub. You get this missile whether you choose to rearm your sub or not. They are yours forever.
Then do the bottom mission: Assemble and Arm AAS. Now you have an armed and assembled Ship!!
Final piece is to go to Nuclear and do the last mission: Arm SCB-304 Submarine and this is you getting your armed sub back.
Process costs you 750 Energy and 162 points of experience. It also costs you $2,000,000 in upkeep per hour per ship.
To recap process: recylce armed sub,arm ship, arm new sub, recycle....