Sound like half-heights, used to be very popular in the 80’s/90’s, did a lot of H/H work for ACL/Cunard, OOCL, ACT, OCL in that time usually used for smallish heavy items, steel for export mainly or heavy but small machinery. Used to pick up 40ft H/H’s out of Houston’s in Renfrew that looked like a third height American style box trailers but inside where 2 x 40ft x 3.45ft tubes that contained Ethanol (Unblended Alcohol) brought down from the Highland Distillery’s for Export to the States, you would never have known these 40ft H/H boxes were actually tankers in disguise. A short anecdote the owner of Houstons of Renfrew was reputedly alleged to have found a way to extract a couple of litres of this ethanol without damaging the Customs sealing methods, and mix up a good brew of Scottish Moonshine, however true it was nobody will know but whenever I went in his yard ‘Big Jock’ was always ■■■■■■ but friendly and very funny in a Scottish way 
Regards
Dave Penn;