Strike Witches Zero:1937 Fuso Sea Incident is a ongoing manga series being released in Nyantype magazine. It is illustrated by Ningen.
The story follows Sakamoto Mio as she receives training to become a Witch from Kitagou Fumika. The plot will later shift to the Fuso Sea Incident as the story progresses.
(Source: Strike Witches Wikia)

The Sky That Connects Us, often referred to as "Strike Witches 1.5", is a manga that was published in Nyantype magazine. Additionally, a Tankouban version with all eight chapters was published by Kadowaka at the end of September, 2010. It spans the time between the two seasons of the Anime. It covers the activities of the various members of the 501st after it was disbanded following the destruction of the Neuroi Hive above Gallia.
(Source: Strike Witches Wikia)

This story follows the earlier career of star Suomus witch Eila Ilmatar Juutilainen, when she was a part of the Suomus Air Force, 24th Unit.

"Noblesse Oblige" - The obligation of nobles. This addition to the World Witches franchise focuses on the 506th Joint Fighter Wing; a squadron of witches tasked with protecting innocent people from the Neuroi following the liberation of Gallia. These Witches are referred to as the "Noble Witches" because of their social status and their dedication to serving the needs of the less fortunate.