File:SM U-21 (Austria-Hungary).jpg
{{Information
|Description={{SMS|U-21|Austria-Hungary|sub=y}}
|Source=http://freenet-homepage.de/kriegsmarine/u20-u32.htm
|Date=c. 1915–1918
|Author=Unknown
|Permission={{Non-free watercraft image|SM U-21 (Austria-Hungary)|image has rationale=yes}}
}}
{{Non-free use rationale
| Description = Image of SM U-21 (Austria-Hungary)
| Source = http://freenet-homepage.de/kriegsmarine/u20-u32.htm
| Article = SM U-21 (Austria-Hungary)
| Portion = cropped to focus on the submarine
| Low_resolution = yes, the image is smaller than the size published at the source
| Purpose = to identify the subject of the article in question
| Replaceability = No. The submarine was scrapped in 1920, and thus, is unavailable for further photography.
| other_information = This photograph may, in fact, be public domain, but without knowing its publication history (other than the source listed above, the publication history is unknown) or the photographer (unknown), no determination may easily be made.
}}
{{Non-free use rationale
| Description = Image of SM U-21 (Austria-Hungary)
| Source = http://freenet-homepage.de/kriegsmarine/u20-u32.htm
| Article = U-20-class submarine
| Portion = cropped to focus on the submarine
| Low_resolution = yes, the image is smaller than the size published at the source
| Purpose = to serve as a representative example of the submarine class
| Replaceability = No. None of the submarines of the class were extant after 1920, and thus, none are unavailable for further photography. While there are free images of the Havmanden class submarine (1911) upon which this class was based, the Austro-Hungarian design was different.
| other_information = This photograph may, in fact, be public domain, but without knowing its publication history (other than the source listed above, the publication history is unknown) or the photographer (unknown), no determination may easily be made.
}}