British WWII Addressee Reported Missing Returned Envelope

Here is a interesting item from my stacks I thought I would share.
It is a Great Britian "Return to Sender" envelope.
Sender mailed item from Walthamstow on 18 June 1940.
Envelope has a Field Post Office 377 cancel 5 September 1940 on flap.
Under the return label is a "7th Battalion, Royal Sussex Regiment" initialed oval handstamp. As well as a Reported Missing handstamp.
On the label the address was supplied by the letter inside, and has a "Army Post Office" handstamp, with handstamp that Pt.L.King was reported missing.
Cover also had a G.R. Opened by official sources securing tape.

This is a truely interesting item if you like war material.

Enjoy.