The M-OV P2 is an battery audio output triode with a two Volt filament. The printed oval with the Type designation inside is typical M-OV. The underside of the base is plain and thus does not carry the M-OV letters at the centre.
The envelope is clear and this suggests that this was made after the Azide process was rendered obsolete by better techniques.
With a thin wire filament the thickness of the valve can be small.
The front of the anode. The grid can be seen above the lower mica as can the broken pieces of the filament. Looking at the top the tension springs have fallen off.
The filament was originally formed as an M.
The balloon envelope is 41 mm in diameter, and excluding the B4 base pins is 84 mm tall.
References: Data-sheet & 1043. Type P2 was first introduced in 1930.