The markings are ex-RAF, Tactical Communications Wing (TCW) Ground Support Equipment (GSE). The ALR and Number are from the Ground Equipment Management System (GEMS). So TCW had at least 14 of these, the ALR type code does not stand for anything, it's just the next code in the list. The guys who did the type coding sometimes connected them i.e. the new Air Start Trolley was given the type code AST. TCW spent most of it's life at Brize Norton and is now at Leeming. Mark.