J3

J3, J03, J 3 or J-3 can refer to a number of things:
* J3 Operations Directorate, organized within the US Joint Chiefs of Staff
* J3 type submarine, a WWII Imperial Japanese Navy predessecor of A1 type submarine
* County Route J3 (California)
* GS&WR Class J3, a Great Southern and Western Railway
* HMAS J3, an Australian submarine
* Janko group J3 in mathematics
* Junkers J 3, a German
* Malaysia Federal Route J3, a major highway in Johor, Malaysia
* Piper J-3, a 1938 small, simple, light aircraft
* S/2003 J 3, a natural satellite of Jupiter

and also :
* Northwestern Air IATA code
* J03 : acute tonsillitis ICD-10 code