The International A-Series (or A-line) replaced the S-Series for 1957. The name stood for "Anniversary", as 1957 marked the fiftieth (or Golden) anniversary of International Harvester's truck production. It was largely a rebodied version of the light and medium S-Series truck, incorporating a wide cab and more integrated fenders. A modified version of this truck range was also built in Australia until 1979, where it was marketed both as an International and as a Dodge.


The new lower design necessitated a slight hump in the cabin floor. The new front end and panoramic windshield brought the design more up to date for the later half of the fifties. The hood was now hinged in the rear, rather than being a lift-off unit. The parking lights were mounted above the headlights. As with the R- and S-Series trucks, there was a Travelall station wagon version developed from the new range. There were A-100 to A-180 series models available. The Gross Vehicle Weight ratings ranged from 4,200 to 33,000 lb (1,900 to 15,000 kg).


For 1959, the B-Series replaced the A-Series. This was the first of the series to feature V8 engines as an option, of either 304 ci or 345 ci. The usual engines were International's 'Diamond' series of inline-sixes. The B-series had twin headlights, mounted above each other. The B-120 was also available with four-wheel drive. The B-Series was available with the same weight ratings as its predecessor, and was built until 1961 when more thorough changes took place.


In 1961, the C-series appeared. At first this would have seem to have been another facelift, featuring a modernized front end, but it also meant a whole new chassis with all new independent front torsion bar suspension. The new chassis and suspension allowed for the cab to be mounted four inches lower,[4] meaning an even bigger transmission tunnel hump but also a more car-like ride. The most obvious visual difference were that the twin headlights were now mounted side-by-side, and a new grille of a concave egg-crate design. The wheelbase was longer, as the front wheels were mounted further forward. This increased the front clearance angle in spite of the lower body. The range was C-100 to C-130, the heavier duty versions were not replaced as the C-Series' Gross Vehicle Weight rating now only went from 4,200 to 8,800 lb (1,900 to 4,000 kg).

The Travelall range underwent the same changes as did the light trucks, in April 1961. The C-100/C-110 Travelall now rode on a 119 inch chassis.

The pickups continued to undergo a continuous stream of minor modifications to the grilles and headlight fitment. For model year 1964, the renamed range (C-900 to C-1500) received single headlights. For 1965 the name became the D-Series, followed by the 900A-1500A in 1966, 900B-1500B for the next year, and the last year which was unsurprisingly called 900C-1500C, depending on weight rating. The Travelall was considered a version of the light-duty pickup range, rather than a separate model, until major changes to the bodywork took place in 1969.