Quoted by A Short History of the RSPCA Animal Hostel at London Airport. Pt. 2: International Activities.
Description:

'On New Years' Day 1955, 394 Rhesus macaque were found dead at London Airport. The animals were part of a consignment of 1600 monkeys travelling from Delhi to New York. Having been unloaded from their Delhi flight, they had been placed in a van to be transferred to the next leg of their trip. But the plane to New York hadn't been ready for loading. The driver had removed the van to what the subsequent RSPCA-led investigation called 'a sheltered location' to await embarkation. The vehicle, however, was unventilated. Crowded into their temporary container, the monkeys had died from suffocation as they waited out the delay.

The resulting RSPCA report found 'neither deliberate neglect nor any calculated act of cruelty' on the part of airport operatives, and noted that the British Overseas Airways Corporation personnel responsible had used an unventilated van 'because it allowed the monkeys to keep warm.''

 

From original:

'The veterinary surgeon's certificate in the R.S.P.C.A.'s possession states the monkeys died of suffocation. The duration of their stay in the van was greater than expected because the aircraft was not ready for loading. Whilst the monkeys were waiting to be loaded, the van was removed to a sheltered position. An additional delay arose from the fact that the aircraft entry doors were facing east into a cold wind and the plane had to be turned.

An unventilated van was used because it allowed the monkeys to keep warm.

The R.S.P.C.A. sees no grounds for prosecution of anyone, since there was neither deliberate neglect nor any calculated act of cruelty. On the contrary, B.O.A.C. officials handling the animals tried in every way to spare the monkeys from harm.'