[Amps] 1 tube or two ??

[kg7hf at comcast.net]

I don't know much about the 4-1000, but the Navy uses (or used to) a pair of 4cx1500b's the output is a little over 1500 watts usually, and I know more can be had...

But most of the communications back when I was in was high duty cycle, so I wonder if maybe the pair of 4-1000's was for something with a high duty cycle?   Maybe rtty, sstv, or maybe even AM?  Would a pair of 4-1000's last a bit longer running legal limit in a continuous duty mode?