Navy Garand rifles were conversions of the standard .30 Garand to 7.62 NATO. There were two versions: the Mk 2 Mod 0 and Mk 2 Mod 1. Mod 0 rifles used the chamber insert to shorten a .30 chamber to 7.62 NATO length. The chamber insert feature did not work well, because no matter what was tried, the insert came out. Three differnent methods were tried to get the inserts to stay in the modified chambers, but all were failures. The chamber insert has never worked in commercial barrels either. Barrels with chamber inserts should be avoided like the plague.
The Navy then contracted Springfield Armory, Springfield, Mass. to build dedicated 7.62 NATO barrels. These barrels were had chrome-plated chambers, bores, and the band around the gas port. Rifles with these barrels were known as Mk 2 Mod 1. Many of the Mod 0 rifles were converted to Mod 1 standard. The converted rifles had the navy nomenclature engraved along the left side below the elevation knob and above the stock.
Both Mod 0 and Mod 1 barrels had their gas ports drilled larger to assure functioning with 7.62 NATO ammuntion.
The other addition to the rifle was a spacer block made of either steel or plastic. The block was attached to the bullet guide. The block acted as a feed ramp for the 7.62 NATO ammunition and as a safety device to prevent loading of clips with .30 ammunition.
Commercial barrels are available to convert shot-out .30 barrels to .308/7.62 NATO. All commercial barrels have short chambers and must be finish reamed by a competent gunsmith for the correct headspace on the rifle. Although the rifle can be shot with .308/7.62 NATO ammo without using the spacer block in the rifle, it is not recommended. There is always some idiot who will try to load a converted Garand with .30 caliber ammo and then try to pound the bolt forward when the round does not chamber.
In either case, .30 or .308/7.62 NATO, the standard Garand 8-round clip can be used in this rifle without any modifications to it.
A genuine "Navy Garand" is a prized addition for collectors and they are typically great shooting pieces.
I have a converted Garand in .308/7.62 NATO and a standard Garand in .30 caliber. I happened to shoot both of them one day and the differences in recoil were interesting. The .30 caliber Garand had a recoil best discribed as a steady shove against your shoulder. The .308/7.62 NATO Garand's recoil was more of a sharp punch. The book says that either cartridge has approximately 15 foot-pounds of recoil which is probably correct. The way it's felt by the shooter is entirely different.