The TSL-20 came out after the TSL-15. The TS-15 was made 1941-’45, with the TS-20 coming out in 1946 according to our Johnson guide book. There is a military manual for the TSL-15 which has about everything you could want to know in it. It has 63 pages in it divided into 3 parts: Operation, Maintenance, and Parts. It is illustrated, and the manual number on the dark green cover is TM5-8002. The -15 is nearly identical with the -20 except for the crankshaft and magneto. The letter ‘L’ in the model number means long shaft.