Duncan,it was H& S that finally saw the demise of the Herc tankers,as the Andover tanks were single skinned,and would be a nightmare if involved in any shooting war,as the system did not allow fuel to be directly offloaded thu` the HDU to a receiver,but transferred up to the main fuel system,not that the rest of the aircraft`s fuel system was any different,ie no self sealing /flame-suppressant system,either...
I took a couple of tankers to the `scrapyard at Marshall`s` `,ostensibly for scrapping,but they were later sold on to the Sri Lankan AF ,and also the Austrian AF..Still in service I think...and they`d been operated at up to 175kMauw......! or thereabouts...
It was never comfortable looking out at the wings/engines`nodding`; one felt that Marshalls should have put a couple of extra `struts/flying wires on the wings....