The best book on the subject is probably Destroyers for Great Britain: A History of the 50 Town Class Ships Transferred from the United States to Great Britain in 1940 by Arnold Hague
Here is his summary of what the Inspecting Officer noted in Halifax (Hague p 11)
The Inspecting Officer reported that, generally, the hulls and main machinery were in good condition, but that the auxiliaries, piping and wiring were poor. All ships suffered from water in the fuel, leading to complete loss of power on several trials. This was though to have been cured by pumping out, tank cleaning and careful fueling. In fact, the problem was more severe in that the contamination arose due to loose corroded rivets in the shell plating, so the danger of contaminated fuel remained with the ships throughout their operational lives. The problem was not isolated in Halifax as dry docking was not carried out.
The attached picture is a graphic depiction of the problem, uncovered after drydocking of Burnham ( ex-Aulick)
As to the changes the British made there were two general programs most of the vessels went through
Stage One done mostly in Devonport comprised of the following
1. removal of the main mast and shortening of the foremast
2. shortening the three after funnels by several feet
3. removing the after 4" and 3" guns and shipping a British 12pdr HA in lieu mounted in X position
4. removal of the two after sets of torpedo tubes
5. fitting British depth charge throwers
6. fitting ASDIC where the equivalent US gear had not been fitted and fitting British trace recorders in all
Stage two condition happened as the war progressed and at different times for different vessels
1. removing the beam 4"guns and fitting single manual 20 mm Oerlikon in lieu
2.removing the remaining (forward) torpedo tubes and installing one triple British mounting on the centre line aft of the funnels
3. fitting type 286 radar at the masthead
4.fitting type 271 radar atop the bridge structure
(Hague p 12-3)
Three of the vessels, Bradford, Clare and Stanley were modified even further into Long Range Escort types. The two forward boilers and funnels were removed and tanks holding 80 extra tons of fuel installed. They also had new British type bridges installed as well as having ASDIC updated.
; thank you very much for this great effort 
. A little query..................
.
when looking at the unavailability figures for the four pipers which remained in the USN, we do not find this large 'extra unavailability'.
