For a while, part of my job in the mid 70s was the planning of the North Atlantic freighters. Inevitably each season we would plan a programme for n aircraft, and end up with n-1 as one of the convertibles would end up on passenger duty.
While our programme could theoretically be done – just – with the assets we had, inevitably things would go wrong and we were forever leasing aircraft, often at very short notice. At one point I was promoted and a rather sweet young lady, fresh out of university, was brought in as my assistant. She proved to be a fearsome negotiator with the airlines we were accustomed to use for these ad hoc charters and got their prices down to well below what I had been accepting, she earned her salary many times over, just on that part of the job.
From hazy memory, there was a longish gap when BOAC didn’t operate West Coast nonstops. In the 60s they had used 436s on San Francisco, which was at the limit of their range – the story went that they would refuel immediately on landing, when the tanks were cold and they could get more in. When Los Angeles was introduced in the 70s I think it started off as a 336 route before it switched to 747s.