This is a Model 100N made by Pelikan Milan shortly after the war.

As for the barrel of the Milan model 100N (and 100Nf), the ink window is shorter than on standard models, and the "sleeve" is longer instead. But, what identifies this fountain pen as a Milan model most is its distinctive barrel. In the case of the standard model 100N from this era, the body was constructed by covering a transparent acrylic resin barrel—integrated with the grip section—with a colored cellulose acetate sleeve; as a result, a step formed between the ink window and the sleeve, corresponding to the thickness of the sleeve. In the case of the Milan-made 100N, the barrel was constructed by seamlessly welding a colored solid celluloid tube—which formed the rear half of the barrel—onto a transparent celluloid tube serving as the ink window and the threads for the cap (this is why the ink window appears to flow smoothly and seamlessly into the "sleeve"). The grip section was made of a different material, cellulose acetate, and was attached to the transparent celluloid tube. Thus, in the case of the Milan-made Model 100N, the body consisted of three parts: the grip section, the transparent ink window, and the colored rear half of the barrel (in the case of the standard Model 100N, it consisted of two parts: a one-piece barrel and a sleeve).

The reason why the Milan subsidiary continued to produce such an elaborate 100N barrel before WWII is unclear. Presumably, by eliminating the steps in the barrel, they were trying to make the barrel's silhouette appear slimmer and more streamlined⁽²⁾.

Whether or not Günter Wagner’s headquarters took a cue from the Milan subsidiary , this trend intensified in 1949, and the grip section became smooth on not only the Milan model but also all 100N models⁽¹⁾. As a result, the rugged step was removed from the grip section, and the body took on a more refined, streamlined shape. This pen exemplified the Milan subsidiary’s dedication to its design⁽³⁾.

The trend in fountain pens had already shifted from angular, sturdy designs to slimmer, more streamlined ones. The following year, in 1950, Pelikan finally launched the model 400 of new style⁽⁴⁾ that had been conceived more than a decade earlier⁽⁵⁾.

Note;⁽¹⁾Based on the smooth grip section and the nib with three lamellae, this pen is believed to have been made around 1949 (in 1950, a feed with four lamellae was introduced).
⁽²⁾It may have been influenced by the streamline moderne style of the 1930s, a style that was popular at the time and is characterized by sleek lines and a minimalist approach to design.
⁽³⁾Looking at the model 100Nf, which was manufactured in the same year, the grip section had no screw threads, resulting in a seamless transition from the grip to the extension. The slim body creates beautiful curves.  It can be said that this fountain pen clearly reflects Milan subsidiary’s design philosophy even more clearly.
⁽⁴⁾The grip section of the model 400 was nearly identical to the modified section of the 100N. Therefore, this is a very rough way of looking at it, but if you were to extend the 100N’s sleeve to the the threads and lengthen the barrel, the resulting shape would closely resemble that of the 400’s body..
⁽⁵⁾The glass negatives in the Pelikan archive indicate that design study for the model 400 had been started in late 1930's (Pelikan Schreibgeräte). However, the development and release of the model 400 were likely delayed due to World War II and the subsequent turmoil.