The Marshall Major
The Marshall 200 was released circa 1967 in response to the need for more power than the 100 watt stacks at the time. The 200 featured active tone controls and was nicknamed a "Pig" by David Bowie's guitar player [Mick Ronson] who swore by them and used his Pigs exclusively throughout the Ziggy Stardust era of late '60s - mid '70s.
In late 1967-early 1968, the front panel and circuitry of the Pig was revised and made wider to be identical in width to the [then] standard dimension of their 100 watt heads. Concurrent with that change, the "Marshall 200" (aka "Pig") was re-named to Marshall "Major".
Note that for both the Pig (Marshall 200) and Major, the height of the box for the head was slightly taller than the standard 100-watt heads in order to accommodate transformers needed for the 200 watt output.