Fitting "for but not with" is a design concept used by militaries in which a weapon or system called for in a design is not installed or is only partially installed during construction to save on construction costs. The term is usually used in regard to vehicles and ships but sometimes extends to all hardware. Items of this nature are usually noted as being "fitted for but not with" or "fitted to receive".

Provision is made for the installation of a weapon or system which is marked for purchase at a later date, with installation during the vehicle's modernisation or refit. This is done to reduce the vehicle's build cost by not purchasing the system at the time of construction, or as a method of future proof

Future proof

The phrase future proofing describes the exclusive process of trying to anticipate future developments, so that action can be taken to minimize possible negative consequences, and to seize opportunities. For more on the process and practitioners, see Futures studies.-Data storage:Electronically...

ing a design. Part of the justification for this design concept is the idea that in the event of the system being required (such as a war), there should be enough warning time to purchase the system, install it in the vehicle, and train operators in its use.

Fitting for but not with can range from leaving sufficient space for any future upgrades, to installing a weapon system during construction but not purchasing ammunition until it is needed.