I've been a Harpooner since my collage days in the early 90's and was delighted to rediscover the game about a year ago.
I see that there are several "might have been" units but there are I few units that "almost were" but didn't get the chance.
I would love to see these units in future updates of the game and that they would add to the enjoyment of all harpooners.
I'd make them myself but I couldn't get my "unit modifier" to ever work.
Units:
F-12B the Interceptor version on the SR-71A Blackbird
A-6F Intruder II advance form of the A-6 with non afterburned equipped F/A-18 engines, new avionics and limited A/A capablity.
A-12 Avenger the stealth attack bomber that was to replace the A-6E
F-14E aka Tomcat21 multi-role F-14 like F-15E
A/FX aka navalized F/A-22
Aurora spyplane the "hypothetical" Mach 6 replacement for the SR-71A Blackbird.
TR-3B stealthy tactical recon/strike plane. Another of those "black program" aircraft that may or may not be out there.