The Marylebone sets, which were later transferred to Bletchley but remained on Chiltern Line duties (and finally to Old Oak Common), were declared surplus after the introduction of Class 165s, from 1991 onwards.

They were, in turn, replaced on this line by Class 117 power twins, displaced from Paddington suburban duties.

Some of the class briefly found their way on to the Redhill to Tonbridge Line to replace ageing DEMU sets.

On 11 December 1981, two four-car Class 115 units were involved in a collision between Gerrards Cross and Seer Green.

The driver of an empty stock train, traveling from Marylebone to Princes Risborough, had stopped in the cutting between Gerrards Cross and Seer Green, to clear tree branches that were overhanging and had fallen onto the track, due to very heavy snow fall.