In October 1982, the first prototype of the modified Mercedes Benz O305 buses for the Busway had been built. The first articulated prototype was completed 4 months later. The rest of the O305 rigids and O305G artics were delivered between December 1984 and May 1986.

Mercedes Benz O305 #1539 was built in April 1985, and entered service 09/03/1986.

In 1994, the State Transport Authority was reorganised and a new body, TransAdelaide, took over the operation side of the STA. In 1996, the bus network began to be privatised, with TA having to tender for the network. TA kept the O-Bahn contract until 2000, when it was awarded to SERCo, a publicly listed British management company.

SERCo renumbered all their buses to be 3 digits. This was done to the Mercedes O-Bahn fleet by removing the first digit, so 1539 became 539. In 2005, Torrens Transit (owned by Transit Systems Australia) took over the O-Bahn contract after Serco withdrew from bus operations. 539 continued to be a workhorse on the O-Bahn until all Mercedes O305/Gs were removed from O-Bahn service in 2010. 539 was one of the last, removed in December.

In 2011 the majority of O305/Gs were transferred to SouthLink (Owned by Australian Transport Enterprises (ATE) at the time) and ran rail replacement services on the Gawler and Noarlunga lines. During this period it was renumbered to R539, then finally retired in April 2012.

In April 2015, R539 was bought to be used as a spare parts shed for the former owner’s preserved buses. However, in 2019 their opinion was swayed to sell it to its current owner, to be returned it to its former glory. R539 was bought for preservation on 11/12/2020.