P-42 or P42 may refer to:
Vessels
- , a corvette of the Argentine Navy
- , a submarine of the Royal Navy
- , a patrol vessel of the Irish Naval Service
Other uses
- Curtiss XP-42, an American experimental fighter aircraft
- GE P42, a diesel locomotive
- Lake City Air Force Station, a closed United States Air Force radar station in Tennessee
- MAPK1, p42 mitogen-activated protein kinase
- Papyrus 42, a biblical manuscript
- Phosphorus-42, an isotope of phosphorus
- P42, a Latvian state regional road
- P-42, a specially redesigned record-setting Sukhoi Su-27 Soviet fighter aircraft
- P4<sub>2</sub>, three-dimensional space group number 77