What is the plural of major-general?

Answer 1

With compound nouns the head noun usually gets the plural form. So:

• two governors general
• two passersby
• two sons-in-law
• two courts martial

Some Army ranks are slightly confusing as the important noun is at the rear, in this case the important noun is General, as in Brigadier-General, Major-General, and Lieutenant-General. They are all Generals. The preceding noun merely denoting whether they are 1-, 2-, or 3-star Generals.

Therefore the plural of Major-General is Major-Generals.

The same rule applies to other ranks (plural of Lieutenant-Colonel is Lieutenant-Colonels and not Lieutenants-Colonel and the plural of Sergeant-Major is Sergeant-Majors and not Sergeants-Major).

Another answer:

The plural of Sergeant Major is in fact Sergeants Major. The noun major modifies sergeant. The same rule applies to Sergeants First Class and Staff Sergeants. Lieutenant Colonels are junior colonels.