Field Major was a Sontaran military rank.
Field Major Styre was conducting experiments on humans on post solar flare Earth after the planet was habitable again. (TV: The Sontaran Experiment) Work on such were published among his kind. (AUDIO: Heroes of Sontar)
Field Major Thurr was leader for some flawed Sontarans which Fleet Marshal Stabb sent as a sacrifice to the Witch Guard on Samur. (AUDIO: Heroes of Sontar)
Kayste held the rank of a field major when he met the Seventh Doctor and Melanie Bush. (AUDIO: Terror of the Sontarans)
Along with a Draconian and a human, Field Major Sarg was transmatted into a cell to fight the other occupants. (HOMEVID: Mindgame)
After landing in Egypt around 3500 BC and being declared a god, Field Major Styx tried to make the natives build an ion cannon emplacement to use against the Rutan Host. While recharging, Tothmes told the pharaoh that the god had died and had him entombed. (COMIC: The Gods Walk Among Us)
Starn was a Field Major attached to Sontaran Military Intelligence. He longed to return to active combat duty, (AUDIO: Silent Warrior) and indeed died a fighting Commander. (PROSE: The Three Little Sontarans, The Three Brothers Gruff)
Kaarsh was a Field Major involved in the Gunpowder Plot of 1605, facing the Rutans led by Elizabeth Winters, after the Rutan ship crashed on the site Parliament would be built on. They were tracking a doomsday bomb that could wipe out an entire species. The conflict ended in a stalemate as the Eleventh Doctor provided both sides with a bomb that could wipe out either species. (GAME: The Gunpower Plot)