03 or 04 military shunters

[south]

As a young lad i used to spend a lot of time watching trains at a place called st johns lye railway footbridge. This was half way between woking and brookwood on the southwest main line. The time was the 70s and 80s. On 1 very hot day not sure the date but think summer 1980 1981 i sore what i can only describe as an old military shunter in all over green in a bad state. I think it was an 03 or 04 and it was on the up slow line going very slowly pulling a train of condemned wagons about 25 in total. The wagons were making an awful noise. Doze any one know if military trains were allowed on the main line or did anyone else see this or have herd of anything similar please reply.