Several aircraft were, at the height of the cold war, fitted with special chemtrail concentrate distribution tanks, which had to be filled before each sector.

A good example is the F27, where the CCDT was installed at the rear end of the engine nacelle, lengthened for the purpose. It can be seen in the picture below, numbered '45'.

A small electric pump delivered a metered quantity of the concentrate into the engine efflux, controlled from the overhead panel by the F/O. Instructions on where to do this would be provided with the Flight Plan documentation, and destroyed after landing.

Many larger aircraft, such as the BAC 1-11, Viscount, Valiant and even the VC10 (perhaps not all) had the same facility. Certain US-built aircraft were similarly fitted out, and over-enthusiastic crews would occasionally start chemtrail spraying at VR, or even at the start of the roll, as seen in the B707 picture below.

[img:left][/img]

Thanks for the info!