Many WWII fighters had such modification - the goal was the improved backward field of view. However, the dorsal spine wasn't there for nothing - it provided better aerodynamics via better airflow behind the canopy, reducing total drag of the aircraft. Nearly all pre-war aircraft designs had it because of a bit higher speed, but the actual war, as it usually does in human history, set the priorities differently.
In the beginning of the war two Axis design bureaus tried a different canopy and rear fuselage design: there were Focke-Wulf Fw 190 designed by Kurt Tank and Mitsubishi A6M Zero designed by Jiro Horikoshi. They weren't the first fighters with bubble canopies and without a dorsal spine behind, but they were the fighters that were quite numerous and affected the air battles on either side of the Earth. The bubble canopy without the dorsal spine affected the aerodynamics negatively, but it gave the pilots much better view backwards - this was noted not only by them, but by their adversaries as well, since an air engagement was usually initiated by a sudden attack from a blind zone.
Soviet engineers created bubble canopy modifications of the existing aircraft in the end of 1942 and in 1943 these models were produced on a massive scale. Their Western colleagues adopted it later and bubble canopy modifications began to emerge in 1944. Bubbletop Spitfire Mk.XIV appeared a year after the initial design, in April 1945.