The Destroyer ship type is an advanced, multi-role surface vessel outfitted with an array of sensory equipment and weaponry to counter threats from the air, on the surface and under the surface. Destroyers are designed with speed as a key quality and can be called to operate independently of the main fleet (when hunting enemy targets) or in support of the main fleet. As such, Destroyers are given offensive and defensive systems to suit a given situation. Due to their rather expensive procurement and operating costs, only a select few navies operate destroyer-type vessels in any useful numbers.
For the purposes of the GFP final ranking, landlocked nations are NOT penalized for the lack of a standing naval force. However, nations with a standing navy ARE penalized for lack of certain naval assets.
Destroyer strength data through 2017.
Sources: CIA.gov, CIA World Factbook, wikipedia.com, public domain print and media sources and user contributions. Some values may be estimated when official sources are lacking.