[dp_burke]

Have you found his entries in the London Gazette and the Flight Global magazine archives?

Thomas Welch HORTON, D.S.O., D.F.C. (59071).

YOu'll need to search for the serial number during the war years period

He seems to have won his DFC while in the RNZAF

1942

Acting Flight Lieutenant Thomas Welch HORTON (N.Z.39920), Royal New Zealand Air Force, - No. 88 Squadron.

1945
DSO

ROYAL NEW ZEALAND AIR FORCE.

Distinguished Service Order.
Acting Wing Commander.

Thomas Welch HORTON, D.F.C. (N.Z.39920), 105 Sqn.

There are no citations in the London Gazette but the Flight Global Magazines have some more details.

You need to search these further yourself.
http://www.flightglobal.com/pdfarchive/index.html

Act. Fit. Lt. T. W. HORTON. R.N.Z.A.F.. No. 88 Sqn.—Fit. Lt. Horton has successfully completed a number of shipping patrols, also other operations, including the brilliant low-level-attack against shipping in Rotterdam on the 28th August, 1941. Throughout, this excellent captain hi* displayed courage, resource and skill high abtflsW'.he average. His aircraft has been repeajeor* hit and damaged by anti-aircraft fire, and. on no fewer than three occasions, he has brottght his aircraft safely back to base after having had one engine rendered useless by enemy action.
The charactor recognition is poor on the page, you'll need to seek it out yourself and transcribe it.

Sqn Ldr. T. W. HORTON, D.F.C., R.N.Z.A.F.,
No 105 Sqn.-Sinre his previous award Sqn. Lor. Horton baa completed many successful sorties during which he has attacked a wide range of argeW He has on all occasions shown great courage and determination and has done much valuable work.