I think this is great concept and overcomes the issue of defining your position with a series of numbers and letters without any inherent check that the coordinate has been correctly received. It also provides an ease three word phrase to remember. However Send.Moon.Fish is very different to Sends.Moon.Fish. The former is in Essex and the latter in Fife which should be obvious of a mis-communication to a first responder. The other issue is that there is no hierarchy which means that Send.Moon.Fish is nowhere near Send.Moon.Dogs which is in Arizona.
From a Defence community perspective, if What3Words is being used by our potential partners then we will need to understand how it works and be able to covert such positions into a more traditional system that can we used in our systems and processes.
It seems the Mountain Rescue Organisation doesn't like What3Words according to the BBC
https://www.bbc.co.uk/news/technology-57156797
However humans can always make mistakes be it numbers or words.
We've built W3W into our software to help Police in UK (and elsewhere). There is a simple interface where (as long as you have the correct licenses) you can supply a Lat/Long and get a W3W back, or supply a W3W and get a Lat/Long, both accurate to 3 metres. It normally works on the web, but for those of us who supply systems that are not connected, you can license the 'dictionaries' to allow the encode/decode to happen offline. And in several languages as well. Great system, and simple to use.
The Royal Institute of Navigation, Solent and South have a webinar on What3Words coming up on Thursday 20th May. Members of the DSA are welcome to join the webinar though the following link:
https://rin.org.uk/events/EventDetails.aspx?id=1502745&group=
For those unfamiliar with What3Words there is a good explanation with examples on their website: https://what3words.com/about