From The Perry Mason TV Show Book (Revised)
It looks like a case of murder and the eternal triangle. Frank Lawton is an old war buddy of Perry’s who has come out of the woodwork needing to be cleared of the shooting death of his boss, Scott Shelby.

It appears that Perry was busy during World War II. In this episode, the defendant is a buddy who fought beside him on D-Day. In later episodes, Perry reveals that he served on a minesweeper in the Pacific during the war.

Perry mentioned his time on Ulithi with an Air Corps buddy in "Misguided Missile" & his minesweeping in "Traveling Treasure." Mike Bedard 5.5.16.
+ In this episode it is not clear that Perry was at D-Day, he may have just heard Frank's "trouble" later. Fred Flintstone 12/20/2020
++ Raymond Burr "appeared in 'The Duke of Darkness' on Broadway in 1944 before entering the Navy. Mr. Burr left the Navy in 1946," his NY Times 1993/09/14 Obituary noted. Mike Bedard 4.23.15

At various times in his career, Burr and his managers and publicists offered spurious or unverifiable biographical details to the press and public. Burr's obituary in The New York Times states that he entered the US Navy in 1944, after The Duke in Darkness, and left in 1946, weighing almost 350 pounds (160 kg).[4] Although Burr may have served in the Coast Guard, reports of his service in the US Navy are false, as apparently are his statements[73] that he sustained battle injuries at Okinawa.[6]:57–58[74][a]

Other false biographical details include years of college education at a variety of institutions, being widowed twice, a son who died young, world travel and success in high school athletics.[6]:17, 20, 23–24, 40–41 Most of these claims were apparently accepted as fact by the press during Burr's lifetime, up until his death[4][12] and by his first biographer, Ona Hill.[3]:27[b] Per Wiki DLH 6/18/20