In the years immediately following World War II, bus operators in the United Kingdom faced a downturn in the numbers of passengers carried and manufacturers began looking at ways to economise.

The need to minimise the intrusion of the engine into passenger carrying space was a priority, leading to several underfloor-engined single-deck designs.

A prototype was built, STF 90, with a body by Saunders-Roe, to the maximum permitted width of 7 feet 6 inches (2.29 m).

Though two prototypes were thoroughly tested, the same problem of a front-engined bus remained, they had rear entrances with the space alongside the driver being wasted.

An amendment to the Construction and Use Regulations in 1956 saw the maximum length for double-deckers increased to 30 feet (9.1 m), allowing a wider entrance to be located ahead of the front axle.

Leyland took advantage of the new regulation to launch the first prototype Atlantean at the 1956 Commercial Motor Show at Earls Court Exhibition Centre.

A drop-centre rear axle allowed the flat floor, only one step up from ground level, to continue for the full length of the bus.

By 1958, Leyland had overcome most of the problems and moved the engine to a rear-mounted compartment outside the main body and the first production Atlantean PDR1/1, with a 16-foot-3-inch (4.95 m) wheelbase, was launched at the 1958 Commercial Motor Show.

It had simpler mechanical specification than the prototype, with conventional front and rear axles, leaf springs all round and a channel section frame.

[6][7][8][9] Though some operators initially continued to buy front-engined vehicles for reliability, the Atlantean gained multiple orders.

Aberdeen, Bournemouth, Glasgow, Edinburgh, Newcastle, Manchester, Liverpool, Newport, Nottingham and Plymouth Corporations purchased large numbers of the type.

A wide variety of body styles from various manufacturers continued to be offered, allowing the Atlantean to be tailor-made to requirements from operators ranging from the small independent to the large city corporation.

[15] However one AN69 with the 0.690 engine ended up with now defunct operator J. Fishwick & Sons of Leyland, the vehicle having been intended for export to Baghdad.

After the re-organisation, Leyland set out to develop a new rear-engined double-deck bus for the London market to replace the troublesome Fleetlines.

[23] In 1982, SBS ordered another 100 units of Leyland Atlantean, all of which were imported from the UK completely built up with the Alexander L bodywork although there was a cancelled plan to fit one of them with an Eastern Coach Works body.

These buses had a vast improvement in specifications as compared to their older brethren, such as push door control buttons, a new dashboard layout, air circulation systems for use in inclement weather and fully automatic transmissions.

New York's heavily potholed roads also took a toll, and after the Atlanteans spent most of their time being repaired before the fleet was quietly withdrawn in 1980.

Australian Pacific Tours, Kirkland Bros Omnibus Services of Lismore, Sita Buslines and Westbus of Sydney among the operators.

[35] In April 1974 a PDR1A/1 chassis originally intended for Southampton Corporation but fire damaged at East Lancashire Coachbuilders was bodied by Pressed Metal Corporation as a single deck bus for Seven Hills Bus Co.[35][36] Atlanteans were also exported to Baghdad Passenger Transport Services (600),[37][38] Córas Iompair Éireann (840),[39][40] Jakarta (108),[41] Kuwait,[42] Manila (22),[43] Portugal (130)[44] and Storstockholms Lokaltrafik (50).

[45] Though the Atlantean was the first high-volume rear-engined double-decker on the market, Daimler was quick to catch up with its Fleetline model.

Supply problems at Leyland did not help matters and products such as the Scania Metropolitan and Dennis Dominator began to make small inroads into the rear-engined market, while the Volvo Ailsa B55 reintroduced a front-engined double-deck chassis, with a front entrance, with some success.