Sending a telegram used to be the best way to get a message across quickly. In the age of the (steam) ship it could take weeks or months before normal mail arrived. Airmail was faster of course, but even that could still take quite some time. The telephone was an option from the early 20th century, but even as late as the 1960s many people did not have a telephone in their houses. Therefore, to send a short but urgent message, a telegram was often the best way until the late 1960s.
The (Dutch) telegram forms used after the Second World War are not particularly scarce. For most countries it is quite easy to collect them, especially in used form. But some of these widely available forms on closer inspection show something less common. Here is one such example.