ASV Mk 21 Bearing Marker Unit

[redsetter]

One for old Shackleton hands. I've seen a few references to the ASV Mk 21 Bearing Marker Unit, but have not managed to find a good explanation of what it actually did and how it was used. Can anyone recall details ?

[pmills575]

It was used to get a very accurate bearing on a target. The unit had a knurled knob which when pushed replaced the normal trace coming from the resolver synchro in the scanner, by one generated in the Bearing unit. With this trace on the screen the knob was turned until it intersected the target, a small window on the unit then showed the bearing. The screen on ASV was north stabilized with information from the compass.

pm575

[redsetter]

Thanks pm575

[denachtenmai]

resolver synchro in the scanner,

Ah, the infamous ARU I assume, the nightmare change which, if not very careful, because one couldn't see the bottom bolts and had to do them by feel, resulted in a 2BA bolt down the scanner well