Paul,

The Halifax was designed from the outset with air cooled radial engines, not the Merlin, That’s why the Merlin engine installation looks to be like an afterthought and caused so much drag.

There was one experimental Halifax with underslung nacelles and using higher powered Merlins which gave much better performance but the Halifax III with Hercules engines was considered to be a better option.

So the Air Ministry was partly to blame for the dissapointing performance of the early Merlin engined Halifaxes by forcing HP to use engines the airframe wasn’t designed for.

Cheers

Cees