If you liked the Strike Witches TV anime, the Anime-Planet community thinks you'd like:
Henrietta is a young girl who works for a "welfare group" that does the government's dirty work. Cybernetically-enhanced and specially-trained, she is one of a group of elite hit-girls, remorseless killers with no memories of their past. Jose, her partner, has taken care of her since she was brought into the organization following the murder of her family, and struggles between his affection for her, and his opposing duty to his employer. But, time is running out.. for with each bullet they fire, Henrietta and the other girls lose a little more of their humanity.
In both series, some young girls of various ages are trained and supervised by over graded members of an association for which they work for, in order to fight against a common ennemy. (Terrorists in Gunslinger Girl and Neuroi in Strike Witches.) In each of the series, the girls fight using overpowered abilities that they gained due either to their modified body (cyborg like...) in Gunslinger Girl or by using their magic power to operate "striker units" which it's the case in Strike Witches.
On February 10, 1904, Japan entered a war with Russia; but Japan, in order to turn the tides, must destroy the Russian Pacific fleet before it is able to bring reinforcements. Battling on the front lines are brave men and women, and a secret team of specially-trained young girls who can control Raimu spirits with their will: the Raimu Unit. Enter Shintaro Umakai - a teacher who has accepted a job aboard the battleship Amanohara to teach the Raimu unit; however, Shintaro discovers his job has far more duties than he first anticipated: he must have sex with the young Kuki so the ship can awaken, he must dodge the sexual advances of his students, he must avert his eyes from Momen's constant accidental panty shots, and most importantly he must assume the role of their new commander once their old one is whisked away by the enemy. There's a war going on - what's a guy to do?
Military, war of some kind, and specially-trained young girls are the only ones fit to do the job. Lime-iro Senkitan is slightly more ecchi than strike witches but i'm sure you'll enjoy one if you liked the other.
Arika Yumemiya is a poor yet energetic girl who has come to the city to become an Otome – a female warrior with the power to match an entire army. She quickly befriends her irritable fellow student Nina Wong and Princess Mashiro, the queen-to-be. With the help of her mysterious benefactor and abundant natural talent, she’s able to overcome the trials of everyday life in the competitive Garderobe Academy, but darker schemes are afoot. How will her new friendships fare, when secrets of the past and present are brought forth to spark a fight for the crown, and more?
In the future, a devastating event known as Second Impact has destroyed Tokyo as we know it, giving rise to Tokyo III - a city under siege by mysterious lifeforms known only as Angels. Mankind's only line of defense are the Evangelions, a set man-made machines piloted by a trio of fourteen year-old teenagers, Rei, Shinji, and Asuka. The fate of Japan and the entire world now lie with these three children, though they might not have the power to save the most important thing of all: each other.
In both series, chosen peoples (Only girls in Strike Witches.) that can operate special devices (Mecha in Evangelion and the "striker unit" in Strike Witches.) are fighting against "unknown" alien invaders that attack the earth on a regular basis and of which they learn how to deal with even more effectively over the time. Also, in each of the series, we get to learn the past of the characters, the relations between them and also the links that bind them together over the time while they are in "standby" waiting for the next attack to happen.
Both anime have girls fighting against seemingly alien threats that threaten their homeworld, friends and family. Both series provide a high amount of fanservice while still keeping their battle sections lively. Symphogear has however got animation problems but makes up for it with having a very good soundtrack to say the least as it's very musically themed. Strike Witches is less amazing in the musical department but has more conistent animation and a larger cast which receives attention during it's 2 seasons.