Remote detonation in 1960s

[sixties]

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

[Hero999]

Yes, I'm pretty sure it was possible, even back then.

[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

[Hero999]

The easiest way would've been some kine of tone detector system. The device calling the bomb would send a tone of a certain frequency which would trigger the explosion.

[Silent Jack]

If radio controlled airplanes were possible back then.  I would think it would make more sense to use a remote detonator of that variety.  Once they'd phoned or radioed and confirmed that their targets were aboard the target craft, they'd just push the button to detonate.  Trying to get a particular tone seems over elaborate with that era of tech.

[Hero999]

If radio controlled airplanes were possible back then.  I would think it would make more sense to use a remote detonator of that variety.  Once they'd phoned or radioed and confirmed that their targets were aboard the target craft, they'd just push the button to detonate.  Trying to get a particular tone seems over elaborate with that era of tech.

That's fine for a manual system, I thought he wanted automatic.

The only purpose of the tone was to confirm that the device calling the bomb wants it to explode. It could easily be made so anything calling it triggers the explosion but that wouldn't be safe.