The 5 inch HVAR saw little use in the ETO. It was a USN development, inspired by RAF air-launched rockets, and the Navy agreed to provide a batch of them for use on P-47's, which went into action soon after 6 Jun 1944. One writer said they must have not been very effective in the anti-tank role, since they were used for only a short time, but in reality the USAAF in the ETO simply ran out of them. Reference the book "Druid's Circle" by Group Captain H.W. Dean, who flew with the USAAF P-47 unit while they were using the HVAR.
The introduction of the 5 inch HVAR almost coincided with the replacement of the A-20 by the A-26. So there would have been few opportunities for the Havoc to use the HVAR and pretty much only in the Pacific.