In June 1948 the Mills Brothers company released a Marine version of their deservedly popular 1.3 cc diesel. This release coincided with the replacement of the aluminium-case Mills 1.3 Mk 1 Series 2 with the significantly upgraded magnesium-case Mills 1.3 Mk. 2 Series 1.
The Mills 1.3 Marine variant retained the aluminium case of the Mk. I version, although this was turned below the exhaust apertures in an identical manner to the machining of the magnesium Mk. 2 cases then appearing. The motovation appears to have been to use up a remaining stock of the now-redundant Mk. 1 aluminium cases. The re-machined case was provided with tapped holes beneath the exhaust openings to facilitate the addition of a pair of bolt-on exhaust stubs - useful in a marine context. The Marine models were sold with these stubs fitted, also being provided with a flywheel. It is not known whether or not they also featured water-cooled cylinder jackets.
Unfortunately, the Marine model appears to have attracted little or no market attention - only some 300 examples were produced. The majority of these were retro-converted back to aero specification, either by their owners or by Mills Brothers. All known examples have lost their flywheels, while the majority have also lost their exhaust stubs. There are no known surviving examples of the Marine model as originally supplied - all of the Mills 1.3 marine units which remain in circulation today are later RipMax conversions.
Unfortunately, this very rare variant somehow acquired the name "Anniversary Model" during the early 1990's, a name which has stuck. The reality is that no "Anniversary Model" was ever promoted by Mills Brothers, nor was reference ever made to such a variant in the contemporary modelling media. The name appears to be the unsubstantiated invention of some imaginative but now-unidentifiable collector! The engine is correctly described as an aero conversion of the Mills 1.3 Marine model of mid 1948.
A more detailed analysis of this matter may be found elsewhere on this website.
