Defendo and Combato are the same thing unless you mean modern Defendo ala Bill Wolfe. Defendu (Gutterfighting) is Fairbairn's system and one of the best Combat systems ever. The real expert on this is Carl Cestari.

A google search will turn up alot of good material from him. Defendo/Combato was designed by Bill Underwood around the same time Fairbairn was forumlating defendu. Underwood was a canadian and quite possible taught at Camp X around the same time as fairbairn. Their systems were designed independantly, however. My take on Defendo is that Bill Underwood was amazing but that stuff is a little hard for us normal folk to pull of. Modern defendo is also a good system but is totally seperate from the other two.

Fairbairn and others expanded on this system to create the Close Quarters Combat system that was then taught to the troops. Bibelende Hkbp Untuk Laptop. This system was built on Defendu, but modified for military applications, rather than police and riot control. Based on his training and knowledge in boxing, wrestling, savate, Jujutsu, Judo and fights he was involved in during his police work, Fairbairn began to develop his own system of hand to hand combat, initially referring it as 'Defendu'.