SKY GIRLS OVA

In the near future, Earth is at war with aliens called Worms. The war leaves the population of Earth decimated, with young men the main casualties. The Worms were beaten back but their re-emergence heralds the creation of a mecha unit called the Sonic Divers, piloted by 3 young girls to counter this threat. (Source: Anime News Network) — Description from AniList community (anilist.co).