With American and European military and political commitments focused attention on the Korean Peninsula for the Korean War (1950-1953), the Swiss Army, in need of a modernized armor corps to contend with the threat of Soviet invasion during the Cold War, could not procure new mounts from their trusted and usual sources. This prompted an internal tank establishment in Switzerland to be formed and, from this, came the first Swiss tank design in the "Panzer 58" (Pz 58). The type was originally outfitted in its prototype form with a British 90mm main gun and then, a follow-up pilot vehicle, featured the British 20-pounder (84mm) main gun. Finalized forms - of which ten production vehicles emerged - were completed with the British 105mm main gun. Production of this tank spanned from 1957 into 1961 and these units ran in operational service from 1958 to 1964 before thought shifted to a more refined design in the "Panzer 61".
Much of the groundwork for the improved Panzer 61 already lay in the completed Panzer 51 which, for all intents and purposes, proved the preproduction form to the Pz 61. The Pz 61 was similarly outfitted with a Mercedes-Benz 8-cylinder diesel-fueled engine (of 630 horsepower) and featured the excellent British 105mm Royal Ordnance L7 series rifled main gun - able to contend with the T-54/T-55 Main Battle Tanks then in widespread circulation. The Pz 61 could manage maximum road speeds of 31 miles per hour and operational ranges of 160 miles - both improved qualities over the Pz 51's 19 mile per hour top speed and 100 mile operating range. Secondary armament included a coaxial 7.5mm machine gun (early versions featured a coaxially-mounted 20mm cannon) and a roof-mounted 7.5mm anti-aircraft machine gun. Six smoke grenade dischargers were fitted to the turret sides in two banks of three launchers for the vehicle to provide its own smoke screen.
The tank was crewed by four as was the case in the Pz 51 - the driver in the front-center hull, the commander and gunner at the right side of the turret and loader at the left (two roof hatches on the turret). Running gear included six double-tired road wheels to a hull side, three track return rollers, a rear-mounted drive sprocket and a front-mounted track idler. Suspension was by way of a torsion bar arrangement allowing for good cross-country capabilities. The hull provided a rather stout appearance in profile, typical of Western combat tanks of the period, while the turret was well-cast for basic ballistics protection. The engine was fitted to a rear compartment in the usual way. By and large, the Pz 61 proved a most conventional combat tank design of the Cold War and, for the Swiss, was classified as a "medium tank" at a time when the "main battle tank" was beginning to take center stage in armor formations of major world powers.
The Pz 61 featured an operating weight of 43 tons and a length of 9.45 meters, width of 3 meters and height of 2.7 meters. Armor protection was through Rolled Homogenous Armor (RHA) measuring some 120mm thickest at critical facings. The main gun was afforded 56 projectiles while some 3,200 rounds of 7.5mm ammunition were stowed aboard for both machine guns.
As the Pz 58 series served primarily as preproduction mounts to the Pz 61, the Swiss government could move quickly in ordering 150 of the latter as the design was a proven commodity at this point. Deliveries of the Pz 61 spanned from 1965 into 1967 and production was handled by Eidgenoessische Konstruktionswerkstaette of Thun, producers of the preceding Pz 51 series. The concern also used the chassis to form the basis of the proposed "Panzerkanone 68" self-propelled gun (SPG) though only four of this type were ever completed due to the Swiss Army decision to purchase American M109s instead.
In practice, the Pz 61 series proved a serviceable vehicle for the Swiss Army though further improvements were quickly envisioned and some of these implemented throughout the tank's active service life. The Pz 61 managed to serve into 1994 which was something of an amazing feat considering the vehicle's 1965 inception. By this time, the improved Panzer 68, the Pz 61's direct successor, was already operating in some number, having been produced from 1971 into 1983 to the tune of 390 units.
From that point on, all indigenous Swiss Army tanks were eventually replaced by the excellent German Leopard 2A4 Main Battle Tank (as the Panzer 87/Pz 87). No Pz 61 vehicles were ever exported.