Here's an extract from my grandfather Eric's memoirs. His initials were "EDM" (hence my interest in that callsign). He was a British army radio officer in World War One. Eric was born in 1890 and passed away in 1976.
This is a description of his unit's training in England before being sent to the front in France. Eric was an officer in charge of a Wireless Telegraphy unit.
"Here men of all ranks, who had never seen a W/T set were being trained to understand, use, and repair them. The officers at least were supposed to become capable of dealing with long distance reception, such as the Atlantic transmissions on 2000 metres wave length for which we had a 500 yard aerial on masts, and transmission and reception on 200-500 metres with portable sets of various ranges from a mile or two up to 50 miles. We knew about "valves" which were being used for "detection" ("rectification") in the longer range sets, and in the cumbersome 3 valve amplifiers in "listening posts", but the short range "trench" sets which were my concern were operated by sparking coils for transmission and carborundum crystals for detection.
"The Trench set, about the size of a small record player, required if possible 100 yards of aerial on two 15 feet masts and was powered by a heavy 6 volt accumulator. The transmission coil of flat "basket" weave had tappings to the studs of a rotary turning switch in the centre of the set. To the left was a powerful "shocking coil", with an interrupter which could be crudely adjusted to a given "pitch" of buzz. To the right was the knob of a condenser tuning the reception coil (coupled to the transmission coil), the crystal holder, and an elaborate Morse key with "shorting" contacts to protect the crystal during transmission. Faults were almost always due to the elaborateness of the key contacts or a dud crystal. Effective range in open conditions was a mile or two but almost nil in wooded country. The more powerful Wilson set, range about 5 miles, had a separate crystal receiver, quite a refined affair, but difficult to tune quickly. In the other box containing the transmitter the necessary sparking system was worked by a rotary interrupter, resulting in a clean high pitched note. Altogether quite effective but very bulky and using so much current that batteries only lasted a few hours. Effective range meant that the signals were "R7" or at least "R5", that is they could be heard clearly in sensitive headphones in a quiet place. No-one mentioned the noise of guns during action."
In Eric's memoirs, there are also some descriptions of his experience once he got to the front but the above gives you a flavour of his technical acuity -- and his memory, when you realise that he wrote his memoirs in the early 1970s. He was a mathematics graduate but ended up in the Civil Service after the war.
73 de Martin, KB1WSY (for now)