Unidentified Blue Triangle Badge - 2RUR or 9th Infantry Brigade HQ

[Quis Separabit]

Hi

I have been directed to this forum by a member of WW2Talk forum as I have a query relating to an unidentified badge on my dad's battle dress (see attached).

My dad was commissioned to 2nd Battalion Royal Ulster Rifles as Lieutenant in 1943 and later that year was attached to 9th Infantry Brigade Headquarters as Camp Commandant/Defence Platoon Commander before landing on Sword on D-Day.

After travelling through France, Belgium and Holland he ended up near Bremen at the end of the war and in November 1945 was I believe appointed as "Town Major" with Control Commission of Germany in Kassel.

In February 1946 he was promoted to Acting Captain with Control Commission of Germany in Bad Oeynhausen.

I know Red/Black triangle and 2 stripes relate to Third Division and 9th British Infantry Brigade respectively, but have no idea what the dark blue triangle at the bottom relates to?

Looking at his photos from April/May 1944, it appears that:
- at least one other of the 9th Brigade (non RUR) officers may have one as well (third from left on front row)
- in the Defence Platoon photo, some of the RUR soldiers on the back row seem to have a similar badge, though those (non RUR) on the other rows don't?

Can anyone shed any light on this please?

Many thanks.

Quis Separabit