Like their counterparts, the Major Case Response Team in Washington D.C, the people associated with the NCIS: Office of Special Projects also carry firearms for protection and in case they come under attack while they're in the field.
Deeks with his Beretta 92FS in the Season 1 episode, "Fame".
Sam with his SIG-Sauer P228 in the Season 1 episode, "LD50".
Callen with his SIG-Sauer P228 in the Season 1 episode, "LD50".
Kensi with her SIG-Sauer P228 in the Season 1 episode, "Hunted".
For the first two seasons of the show, G. Callen, Kensi Blye, Sam Hanna, Dominic Vail are seen wielding SIG-Sauer P228s. NCIS Director Leon Vance also uses one during Episode:Killshot while Los Angeles Police Department Detective Marty Deeks uses a Beretta 92FS.
From Season Three, Callen, Hanna, Kensi and NCIS Assistant Director Owen Granger are seen using new model SIG-Sauer P229 with the redesigned slide and new grips.
During an undercover assignment in Episode:Neighborhood Watch, Kensi uses a SIG-Sauer P238.