A disciplined way to use alternate history

Does alternate history simply romanticise a cause?

It can be useful when it changes one or two defined conditions and follows their consequences; changing everything at once becomes fiction rather than analysis.

Alternate history remains useful when it starts from clear initial conditions. An earlier workable Royal Navy 4.5-inch upper-deck mount is a bounded change that could influence destroyer armament, refits and later wartime capability. Following those linked choices exposes why actual procurement compromises emerged.