sixties

How would it have been done? In this plot the murderer wants to phone a yacht to make sure a party of people are going ashore in the launch together. Once assured that is the case he phones the device aboard the launch and the launch explodes. What sort of technical detail would be involved? I don't need a step by step breakdown, just some accurate stuff about what was used so it worked and the plot seems feasible. The incident is meant to have taken place in the Bay of Islands NZ. I want the story to have at least superficial veracity. Thanks

Would it have been possible in the 1960s to telephone a device in order to set off an explosive device? Today you can do that with mobile phones. In the plot the objective is to telephone a seagoing vessel and blow it up. Thanks