It seems Vengeances belonged to No 23 Anti-Aircraft Co-operation Unit.
Vultee Vengeance in Italy
Re Polish decoders
Following evacuation from Poland, they approached British embassy but were refused of help and turned to the French. Supported by Maj. Bertrand they decoded messages in France and then established secret decoding centre Cadix, where they tackled with German messages, then send to the UK. Ultimately ended in the UK, but not allowed to Bletchley. I do not know British reasoning behind this.