The early PT boats were not fitted out with radar; after his four-month ordeal in the Phillipines, Lt. John Bulkeley saw the need for radar on PT's, and he lobbied hard for twelve aircraft sets to be mounted on the boats of his new Squadron Seven before it sailed to the Southwest Pacific in 1943. By all indications, this stop-gap measure was by no means successful--the power supply was often faulty, causing the sets to fail at any given moment. Purpose-made radar for the PT's were still some time off, but even before Ron Seven arrived in New Guinea, a few tests were being done in the field.
When PT's 22,24,27, and 28 of MTB Squadron One were detached from the parent squadron at Pearl Harbor and transferred to the Aleutian Islands as MTB Division One, PT 28 was selected to be fitted with an SCR-521 aircraft radar in September 1942, to help the divivion navigate through the fogs prevalent in the area. The SCR-521 (also known by its Navy designator, ASE) was intially installed in various USAAF and USN aircraft for anti-submarine work.
In the Solomons, PT 109 was selected twice to be the test bed for field radar experiments also using the SCR-521, first in December 1942, and again in March 1943. The December tests were judged to be "inconlusive", while the March 1943 tests were a complete failure. Unfortunately, no photos exist of 109 in either configuration--or if they do, they have not surfaced...yet. The radar unit was long gone from 109 by the time Lt. j/g John Kennedy took command of the boat in April 1943...and I'm pretty sure he'd wished he'd had it aboard his boat a few months later...
Below: These three photos show the exterior and interior of PT 28's radar installation, October 1942. PT 109's was similar, but the antennas were mounted on the foredeck. (National Archives, PT Boats, Inc.)
Above, a PT heads out for a night's patrol in New Guinea. Behind her mast can be seen its SCR-517 radar set--the canvas covering protects the sweeper gear. Below, boats of Squadron Nine loaded on SS White Plains in New York in December 1942 for shipment to Panama. The SCR-517 dome can be seen on the first two boats from the left in the foreground (PT 155, PT 152). Originally developed for USAAF B-24 Liberators on U-boat hunting duty, the SCR-517 was adapted for installation in several Elco 80-foot PT's in late 1942. (National Archives)
Below is a much-seen photo of four Elco 80-footers (PT 131 is on the left) moored on the Morobe River in New Guinea in July 1943. The boat next to PT 131 appears to sport a different mast than what is normally associated with early Elco 80-footers...(National Archives)
Above is an image of another boat, taken around the same time, with a similar mast. (National Archives)