[2] With a style inspired by the Englishman Nat Gonella, he guested in 1938 in leading orchestras such as Hot Dogs and Funny Boys [no].
[4] After trips to England (1938–39) with Vic Lewis and George Shearing, he was a central part of Oslo's swing-jazz milieu, where he led his own Rowland Greenberg Swing Band (1939–41) with Arvid Gram Paulsen on sax, Lulle Kristoffersen [d] on piano, and Pete Brown on drums.
He also led his Rowland Greenberg Rytmeorkester (1940–44), with Gordon Franklin on tenor sax, Arvid Gram Paulsen on alto sax, Robert Normann on guitar, Kjell Bjørnstad [d], Frank Hansen, Lyder Vengbo [d] on trombone, and Fred Lange-Nielsen on bass.
A record release (1942) was banned by the German regime, and he was jailed for breaching the Rytmeklubbforbundet by viewing jazz films (1943).
Greenberg took part in the "All-Star Trumpets session" (Paris Jazz Festival, 1949) with Miles Davis, Bill Coleman, Jimmy McPartland and Aime Barelli.