MIDLAND PULLMAN Mk3 FIRST CLASS OPEN COACHMIDLAND PULLMAN Mk3 FIRST CLASS OPEN COACH Mk3 coaches entered service in 1975 along with the Class 43 forming the iconic InterCity 125 trainset. After the HST Mk3 coach variant was introduced, further Mk3 coaches were introduced to the West Coast Mainline for use as part of locomotive hauled trains. Whilst Mk3 stock is standard for HST units, the standard locomotive hauled stock is Mk3a. Mk3a stock differs from Mk3 stock due to the inclusion of