SIW meaning in General ?

The Silver Wraith was the first post-war Rolls-Royce. It was made from 1946 to 1958 as only a chassis at Rolls-Royce's former Merlin engine plant, their Crewe factory, alongside the shorter Bentley Mark VI. The Bentley too was available as a chassis for coachbuilders but also for the first time could be bought with a Rolls-Royce built standard steel body.

It was announced by Rolls-Royce in April 1946 as the 25/30 hp replacement for the 1939 Wraith in what had been their 20 hp and 20/25 hp market sector, that is to say Rolls-Royce's smaller car. The size was chosen to be in keeping with the mood of post-war austerity. Even very limited production of the chassis of the larger car, the Phantom IV, was not resumed until 1950 and then, officially, only for Heads of State.

Improvements announced were: chromium-plated cylinder bores for the engine; a new more rigid chassis frame to go with new independent front suspension; and a new synchromesh gearbox. Chassis lubrication was now centralised.