Marlin has manufactured machineguns and submachineguns for the US Military, as well as making M1Garand barrels, and parts for M1 Carbines.
The Marlin model 1893 with the serial number you provided was made in 1901. It is one of the first ever lever action rifles and it is also one of the most accurate rifles of it's time.
Yes the Marlin model 336 in 356Win.caliber has the Micro groove barrel.It should be noted that there were only 1,652 model 336 rifles in this caliber that were ever made.
the remington model 510 is a 22 plinking rifle used by adults and youth alike. they were not known to have been used by the military, but it's possible.
no, they would use their own security forces (MPs) for any trouble requiring a bunch of guys with assault rifles. how ever if the military turns over control to you maybe but unlikely
the Glenfield name used on the marlin rifle was for mass-merchandisers and chain stores that wanted brand name products to sell. this model you have was made by marlin from 1966-1970. marlin made two variations of this rifle, the change coming in 1969. it should have impressed checking on stock and forearm. As for the JM on the barrel, this is Marlin trade mark. 77,603 were built. these sold for around $100 when they were new. They are real nice rifles, I have a 30A 1st. variation that should look almost like yours except the magizine tube is full length. I wouldn't call it rare, its worth what ever you can get out of it. good solid rifles made by Marlin!
No not that I am aware of.
No
I cannot find any reference to marlin ever making a model 226.
Yes
Finland in the country responsible for the manufacturing of Sako Rifles. Sako Rifles are essentially used in sporting and hunting activities ever since 1921.
no he was not in the military
Standard infantry rifles did not, but there were scoped rifles used for sniping during WWI.