The SL-X-15 (1M1) N1-L3 was sent to the pad from the MIK Building in June 1968 through the end of August 1968 for guidance alignment testing and mockup testing.
The 1M1 was painted with all gray first and second stages and a gray and white third stage and all white L-3 payload as previously seen on N1-L3 (4L), for which no pictures are available from the Corona collection.
The first flight booster '4L' was sent to the east 'J' complex pad on May 7, 1968 for extensive testing and a planned September 1968 flight test. The first stage LOX tank developed extensive hairline cracks. Subsequently the booster was removed from the pad in June 1968. The booster had suffered a whole series of shortcomings. The Soviets cannabalized '4L's first stage, ultimately scrapping most of the airframe structures. They temporarily substituted the FSLT & TV first stage to continue parallel testing of the N1 and L3 elements of the '3L,' flight vehicle. This was the first major change incorporated into the 1M1, FSLT & TV design. It literally substituted flight hardware for the 1M1's upper stages. This is also when parallel processing of the N1 and L-3 (L-1) elements of the program was introduced in order to reduce the vehicle's processing time requirements. The first planned flight vehicle then became '3L' after it was revised as a result of those tests on 4L.
As early as greater than 28 days before its launch on February 21, 1969 at 09:18:07 UT, '3L' was on its pad in early January 1969. It is suggested to have been on its pad well before February 12, 1969.