U43
U43 may refer to:

Naval vessels 
 , various vessels
 , a sloop of the Royal Navy
 U-43-class submarine (Austria-Hungary), of the Austro-Hungarian Navy
 , the lead boat of the class

Other uses 
 Monticello Airport (Utah)
 Small ditrigonal dodecicosidodecahedron
 Small nucleolar RNA SNORD43
 U43, a line of the Dortmund Stadtbahn