This is an excellent example of a very rare late production M1 Garand with the unusual serial number "01" and has been fitted with an experimental collimator optical rear sight. These sights were tested in the late 1950s and early 1960s and it used a single post, floating dot or aiming circle, that was sometimes illuminated inside the sight. The idea behind a collimator sight was that the shooter was to have both eyes open so that you could track your targets while shooting, increasing hit probability while still being able to see the complete periphery of the battlefield. Basically, these were an early optical battle sight, not unlike ZF 41 sights used by the Germans in WWII or the tactical sights we use today. This version of sight is non-magnifying and has a standard single vertical post reticle with two-horizontal hash marks over the top of the post. The sight has a spring loaded base with the entire sight being installed in the area on the rear of the receiver where the normal sight is located. It has its own elevation and windage knobs built right into the optical sight base. The rifle itself is also quite unusual in that it has standard SA, M1 receiver markings of "U.S. RIFLE/CAL. 30 M1/SPRINGFIELD/ARMORY" over serial number "01". Now we all know that serial number "1" rifle is in the SA museum, so why did they number this rifle "01"? The remaining parts are all original Springfield Armory late production parts that are marked as follows: barrel is "SA F6535448 10-56 A228". The bolt is marked "6528287-SA/YO2" . The trigger housing is marked "656528290-SA" with a stamped trigger guard, "SA-11 marked safety, and a "SA D5546008" marked hammer. The operating rod is marked "7790722 SA". It has a late production wide base gas cylinder with a T-37 prong type flash hider installed instead of the standard gas cylinder lock. It has a standard set of walnut handguards with a nicely figured walnut stock that is a correct M1 Garand configuration with a very faint/partial circled "P" proof in the pistol grip area. It was retrofitted with a hinged M14 type buttplate probably for testing of the sight. The stock has a somewhat rounded receiver heel area, a slight notch on the right side, and the low comb area and the more oval pistol grip area all indicative of a late SA manufactured stock.