Martin P4-M Mercator.

1) I read that 21 of these were built, for ELINT and SIGINT between 1950 and 1960. Where were they based?

2)They also said that the aircraft had jet engines in the nacelles.Any idea which engines?

3)They were built by Martin. I’m assuming this means Glenn Martin and not Martin Marietta?
Thanks!
________
Half-baked