Original Panther II turret: “Turm Panther 2 (schmale Blendenausführung)” H-SKA 86176 dated 7 Nov 1943. (Source: Panzer Tracts No.5-4)
Panther I turret designed after Panther II cancellation: “Turm-Panther (Schmale Blende)” H-SK 88517 dated 1 Mar 1944. (Source: Germany’s Panther Tank, The Quest for Combat Supremacy”
Rheinmetall had been tasked with designing the Panther II turret. This new turret was named ‘Turm Panther 2 (schmale Blendenausführung)’ (English: ‘Turret Panther 2 (narrow mantlet variant)’). The cancellation of the Panther 2 project came in May 1943, but Rheinmetall continued their work, with their turret now destined for the original Panther.
Rheinmetall’s progress was sluggish, as 1 year later, they had not yet progressed beyond the drawing stages as evidenced by drawing H-Sk 88517 “Turm – Panther (schmale Blende)” (English: ‘Turret-Panther (narrow mantlet)’). New requirements were drawn up for a new iteration of the regular Rheinmetall-designed Pantherkampfwagen V Panther turret. An Entfernungsmesser (English: ‘rangefinder’) was to be incorporated into the turret and the gunner’s sight was to be changed to a periscope in the roof. Rheinmetall’s design incorporated the Entfernungsmesser in the turret, but this created a huge hump in the turret roof.
It appears this design, combined with the long time already used with no practical results, prompted Wa. Prüf. 6 to move responsibility for designing a new turret from Rheinmetall to Daimler Benz. It seems about nothing from the Rheinmetall’s Turm – Panther (schmale Blende) design was used by Daimler Benz for their Schmalturm design. By 20 August 1944, the first Versuchs-Schmalturm was mounted on a Panther Ausf. G chassis.
The development of that turret was continued after the Panther II got canceled, as a upgrade to the normal Panthers, and it’s pretty obvious it’s a predecessor for the Schmallturm.