138 Heavy Anti-Aircraft Regiment RA(TA) was formed at Llanion Barracks, Pembroke Dock in November 1941. The Regiment was disbanded in October 1945 at Hartlip, Sittingbourne, Kent.
| Nov 41 | Formed | Pembroke Dock, Dyfed, UK |
| Nov 41 | 61 Anti-Aircraft Brigade, 9 Anti-Aircraft Division | South Wales |
| Aug 42 | 67 Anti-Aircraft Brigade, 11 Anti-Aircraft Division | Birmingham, UK |
| Sep 43 | 3 Anti-Aircraft Division | UK |
| Mar 44 | 102 Anti-Aircraft Brigade, 2 Anti-Aircraft Group | South East England |
| May 44 | 5 Anti-Aircraft Brigade, 6 Anti-Aircraft Group | Portsmouth, Hampshire, UK |
| Aug 44 | 43 Anti-Aircraft Brigade, 2 Anti-Aircraft Group | South East England |
| Sep 44 | 5 Anti-Aircraft Brigade, 2 Anti-Aircraft Group | Southern England |
| Mar 45 | 28 Anti-Aircraft Brigade, 9 Anti-Aircraft Group | East Anglia, UK |
Batteries
| Dec 41 | 419, 424, 438, 474 |
| Apr 42 | 419, 424, 438 |
| Jul 42 | 419, 424, 437, 438 |
| Feb 45 | 419, 424, 437 |
