Learn English – When was the term “idiot box” coined

I don't think the Angles landed in the British Isles and said:

"Let's call our language Ænglisc now that we moved to this new land!"

Before they migrated, and that took many years, their homeland was already called Englaland or even Engla and they already named their Germanic language Englisc. The only difference is that this place was Angeln in the south-east part of Schleswig, in present-day Germany.

So to answer your question, the word English was used before England was called England but at that time the word England (or its ancestor) already existed. It was just used to designate a completely different place.

As for the English people the Angles themselves were collectively referred to as Engelcynn (as in kin) or Engelfolc (as in folk, German volk).

Actually Etymonline suggests that the first use dates back to 1917 and is referred to trucks loads while its military application was later, around 1936.

Payload (n.)

also pay-load, 1917, from pay + load (n.). Originally the part of a truck's (later an aircraft's) load from which revenue is derived (passengers, cargo, mail); figurative sense of "bombs, etc. carried by a plane or missile" is from 1936.

Ngram shows that military payload has gained currency by the mid 40's and that suggests that the probable origin is from a truck's load.

The increase in use of the term in the 60's is hard to detect since unluckily Ngram does not help from a semantic perspective. Aircraft payload, passenger payload or industrial payload don't show significant increase in that period.

• Further research ( with the help of StoneyB) shows that actually the term is much older. Paying load" vs "dead load" is found in discussion of railroad freight as far back as 1849 and becomes "pay load" by 1903 where it refers to naval vessel's 'pay load' as its armor and armament.

It is also interesting to note the current meanings of payload:

• payload(Noun) That part of a cargo that produces revenue

• payload(Noun) The total weight of passengers, crew, equipment and cargo carried by an aircraft or spacecraft

• payload(Noun) That part of a rocket, missile, propelled stinger or torpedo that is not concerned with propulsion or guidance, such as a warhead or satellite.

• payload(Noun) The functional part of a computer virus rather than the part that spreads it

• payload(Noun) The actual data in a data stream.