Hi
I found this in one old Polish book by T.Burakowski, A.Sala "Rakiety i pociski kierowane" (Rockets and guided missiles) published in 1960. Probably this is "Ursel":
I try to translate text:
Pic.354. Unguided rocket missile cal.165 mm "underwater-to-underwater" class: 1 - warhead; 2 - solid rocket fuel; 3 - tube for directing forward the combustion gases for reducing the friction of water; 4 - exhaust holes for combustion gases; 5 - nozzle; 6 - fins; 7 - fuselage
Very short description is in the text on the same page:
The picture 354 shows the typical unguided missile this kind. His lenght is 1,8 m, diameter 0,165 m, fins span 0,3 m. It could be stress that for reduction of friction between the missile's fuselage and the water in which the missile move, a part of combustion gases is directed forward by a special tube; on the top of ogival missile are small exhaust holes for these gases. When the missile move in the water, between the fuselage and water arise a thin layer of combustion gases.
And this is picture from the other book by Burakowski and Sala, "Rakiety bojowe" (Combat rockets) from 1972:
The text is:
Caliber 165. Germany - 1-stage rocket missile, submarine-launched, against submarines and surface vessels, underwater-to-underwater and underwater-to-surface class. Unguided. Warhead: conventional. Engine: solid rocket. Dimensions: L=1,8 m, D=0,165 m, B1=0,3 m. Probably not used in combat.
Although Burakowski and Sala do not mentioned the name "Ursel" anywhere, looks that it could be this missile. Dimensions are correct and the technical details (gas tube for drag reduction) are consistent.