Sadder-Krupp's the richest and most powerful megacorp on the earth owned and run by the most powerful being on the earth. Yeah, they have a couple aircraft carriers, they can afford it, it's not the U.S. Navy. Mitsuhama has one supercarrier, but they're practically an extension of the Japanese Imperial Navy. Most of the Big 10 don't have anything like a major nation's military power. They have military assets in case they need to protect corporate assets in a civil war, need to pressure a small country, need to flex against another megacorp, etc.
We're talking for most Megacorps brigade strength at best, with most at company or battalion strength and only the ones with the highest military rating reaching division level. Even the armies of the UCAS, much diminished when compared to the old USA, still has military assets greater than all the Megas combined. The only one that's hard to gauge is Aztechnology, since it's impossible to draw the line between Aztlan the country and Aztechnology the corp.
Monsanto in 2020 currently has larger military assets then some Megas.