The RN broke ratings up into three classes for uniforming purposes. Class II were ratings who wore standard square rig, but classes I and III covered Chief Petty Officers, Petty Officers and those seaman who didn’t dress as seaman such as clerks. This classification covered many different orders of dress including white tropical uniform such as this tunic:

The jacket was single breasted, with a loose cut and a high mandarin collar secured with two hooks and eyes:

The jacket has two open topped patch pockets on the breast:

The jacket has a simple label sewn inside with the sizing and NSN number printed on it:

The basic pattern for the tunic hasn’t changed since before the Second World War, although the number of personnel who could wear it has reduced over the decades as now all seaman below the rate of PO wear square rig and the fore and aft rig is reserved for senior rates.

This particular example has had the incorrect buttons fitted to it, but I will be looking out for the correct ones; they are only held on with split rings so it will be an easy job to swap them o