Different units solve different tasks
A boat sends troops across water to attack a selected location. A warship comes from a port and patrols an area, engaging hostile ships. A missile silo is the launch point for atom bombs, hydrogen bombs and MIRVs. A SAM launcher is a defensive interceptor, not an offensive missile.
This is not a complete damage, price or guaranteed-counter chart. The help describes different interception chances for missile types; a defensive launcher does not make a position immune. Check current range, cooldown, price and mode settings in the game before committing.
Check the action, then the cost
Before a sea action, distinguish moving troops from building a warship. Before a missile action, check the target and whether it can be canceled. The current help says launched nukes cannot be retreated. Do not test an unfamiliar action with resources you need for another objective.