Unusual in that, instead of being adapted to fit the standard slide rest, the Pratt & Whitney swivelling vertical milling attachment was complete with its own compound slide unit - and thus could be used on lathes fitted with were only equipped with the simpler types of hand-tool rest.
The slide carried an indexing unit, of the same collet fitting as the headstock, designed to hold small components whilst milling cutters, diamond laps or grinding wheels, held it the headstock spindle, were applied to them.
A separate high-speed cutter head, driven by an extra pulley on the countershaft and designed to allow work held in the headstock spindle to be machined, was provided as standard.

The powered Filing Attachment - a remarkable Pratt & Whitney accessory and probably unique to a small number of fine-quality American Precision Bench Lathe manufacturers.
Those who have used a "filing machines" will know that they are not what, to the layman, they might seem: a rough and ready method of removing metal, but precisely the opposite. A top-class filing machine was an expensive item - and an experienced operator could achieve almost miraculously accurate results with one. They were not designed to be employed in general workshops but found a valuable niche in better-equipped toolrooms. The unit slid onto the bed and was fastened in position by an eccentric clamp. A tilting rectangular table 4" x 6" was provided as part of the standard equipment

In common with other makers of precision lathes, Pratt & Whitney offered a toolroom-class milling machine which used either the complete headstock from the lathe, or an identical spindle assembly. More details of these machines can be seen here.

A Pratt & Whitney No. 3 with the maker's beautifully-constructed countershaft holding a built-in 2-speed gearbox - similar in some ways to the system used on the Swiss Simonet precision lathe.
If there is one thing that flat belts like, it's plenty of "wrap" onto the pulleys -  which was exactly what the wide, heavy-duty tensioning  system provided on the installation above.

Early and later Pratt & Whitney compound slide rests. That on the left is from a 3c and on the right from the older No. 3. While both follow the same basic design, that used on the 3C has a slightly longer travel on the top slide, and usefully more on the cross. Other refinements include a better oiling system, larger micrometer dials, ball bearings thrust races and travel stops for the cross movement