Adaptation Expansion: The anime shows a battle between Ichiroku against Aug and T91 during the jungle wargame arc.
An episode shows everyone in Seisho Academy preparing for their annual school fair.
Amusing Injuries: After Eru gets hit in the head by Genkoku, she has a large lump on her head. Several scenes later it's still there while Ichiroku's bump has long since faded. It then drastically shrinks after she sits out in the sun for a while.
Pretty much anytime Genkoku gets hurt, helped by the fact that he usually brings it on himself. Until episodes 9 and 10 anyway
Anime Accent Absence: Subverted by Thompson-sensei, who speaks with an American accent, but otherwise played straight by everyone else.
Artistic License - Gun Safety: Proper firearms safety is stressed, and all characters keep their fingers outside the trigger guard when not shooting.
In the live-fire exercise in "Go for it! Pass it!" (also in the manga), the girls were shooting at balloons above each others' heads. Had they been human, this would have been ridiculously dangerous.
Common safety rules are posted in the hallways at regular intervals. The obedience level... is about what you'd expect from middle school students.
A-Team Firing: Happens a lot, particularly in the last episode. Made more blatant by the fact that sometimes the girls are firing at extremely close ranges at targets that aren't using cover.
Bat Deduction: Sixteen realizes that a group of people are targeting her because Eighteen was shot only once while Eighteen's two comrades were shot three times. Eighteen was shot two fewer times; eighteen minus two is Sixteen. That's one obscure way of showing someone you're targeting her.
Blood Knight/Trigger Happy: While several of the high school girls seem to display this trope, the middle school girls can sometimes seem a bit too eager for combat, particularly Sako.
Bloodless Carnage: When the girls get hit by bullets, they don't bleed. Justified because they are guns, not humans. The trope is zig-zagged with Genkoku. After he gets hit in episode 10, a puddle of blood appears next to him. When FNC comments that humans can't be killed by the girls' bullets, the blood disappears. There is no blood when he gets hit again shortly afterwards..
Boom, Headshot: Sako does one as a cheap shot to Sig at the finals of the Jungle warfare tournament. Of course being a gun, all it does is knock Sig over on her face for a moment, mess up her hair and get her really pissed off.
Chapter 24 has G3-senpai getting a couple of these from over a kilometer away, giving FNC and Genkoku some much needed covering fire.
Bottomless Magazines: While the girls are shown switching magazines from time to time, they almost always fire way more rounds than a magazine should be able to hold. Unsurprisingly, they either run out, have their gun jam during plot-crucial points, or in Saiga's case, have their magazine destroyed by someone else's shot.
Break Them By Talking: The climax of the Atami Shootout in the manga has the Soviet Major try this, first on FNC, then on Sensei/Genkoku when he tries to defend her. Since the Major doesn't appear in the anime version of the same events, AK-74 gives it instead.
Breather Episode: Episode 7, which spends time with the girls during the Christmas/New Years holiday.
Censor Steam: Quite a bit of it during episode 9 while the girls are in the bathhouse.
Chekhov's Skill: G3's full auto sniping technique, which Sig later uses against SAKO. L also uses it to keep her magazine in place in episode 10.
Close Call Hair Cut: Sig gets one from Sako, and later returns the favor. Ichiroku/M16 does it as well towards Sako.
FNC gets one as well in episode 9, although it doesn't impact her hair the same it does to Sig.
Cold War: Much of the series' premise, especially the rivalry between Akagane and Seishou, is grounded in it. The series also promotes some really weird Western cliches of the time, like Easterners not helping their wounded (which is said by Nanayon of all people).
Color Failure: Happens to Sensei when he realizes the lady talking to him in episode 9 is Fujiko-sensei without her eyepatch and with her hair down.
Fantastic Arousal: Funco gets this way at the thought of being in the hands of a skilled marksman.
Feuding Families: Being guns from different countries, there are some who have bad histories with each other.
One example is the American guns (M16 and M14) with the AKs (In this case, the Galil and Rk95 as their internals are based on the AK rifles) ever since the Vietnam War. 16 faces the AK faction from Red Steel High later on, which fuels her rivalry with them.
In the manga, there's also the rivalry between the Uzi sisters and MP5 sisters on the best SMG. This has some historical truth to it as a lot of security forces worldwide, including America and Germany, were armed with the Uzi during the Cold War until the MP5 took over as the world's main submachine gun.
And in one omake, MP7-tan and P90-tan face off, reflecting the competition between both PDW types.
Foreshadowing: In episode one, L is laid up in the school infirmary with what the school nurse diagnoses as a bent firing pin. Then, in Episode 3, mention is made of L's various woes when shooting. This culminates in Episode 4, when she breaks her firing pin.
Hair Decorations: Ichiroku has the most obvious one, with a circular orange slice. Sig also has some purple hair clips, and in episode 7, they vaguely resemble cat ears.
Hammer Space: Where the girls can draw their rifles from at any time. Averted for ammo, though.
Thompson sensei uses this in a fight against Aug. Aug kicks Thompson's gun held in right hand which causes it to swing upwards, deflecting her aim. Next instance, said gun disappears from right hand and Thompson pulls out another in her left hand, followed by Boom, Headshot at point blank.
Humans Are The Real Monsters: When Genkoku tries to get the girls and the AKs to stop fighting, 74 points out that humans are the ones that produce guns in the first place.
Human Shield: Ichiroku uses the teacher as one in episode 7 during a snowball fight.
Humiliation Conga: The narrator relating the L85's troubled history, with L confirming that all her bad press is true. And then to cap it off, "Taps" is played. As in the bugle music at military funerals.
And then if this wasn't enough, she breaks her firing pin in Episode 4, after repeatedly put down and referred to as a dud.
Info Dump: Done on a regular basis to give background information as to why the girls act a certain way, or the relevance of a current event, such as Ichiroku's rivalry with Sako.
Instant Bandages: FNC has some in episode 1 when Genkoku accidentally ricochets some cork bullets on her face at a festival stand.
I Work Alone: M16/Ichiroku plays this trope during the tournament in episodes 4-6, due to being teamed up with Eru, who misses the flight to the jungle. Until the finals, she actually manages to hold her own while soloing.
Just for Pun: There's a reason why all the AK-type weapons of Red Steel High have cat ears. The original full pronunciation of the school from its kanji 紅鋼高 (Akaganekou) contains a pun (AK ga neko, or AK is a cat).
Kansai Regional Accent: 16 speaks in Osaka-ben to emphasize that she's loud, boisterous, and fun-loving. Sako speaks in Kyoto-ben while Galil speaks in an Umpaku dialect, spoken in central San'in region, namely Tottori and Shimane prefectures.
Karma Houdini: While Sako loses in the tournament in episode 6, she's never punished for taking that cheap shot at Sig, nor her excessive abuse towards FNC.
Knights Of Cerebus: SAKO in episode 5 and the the AK group that attacks the girls during the school trip in episode 9, it's even stated in the latter case that if Ichihachi had been struck at a slightly different angle she would have died.
Loophole Abuse: In the beginning of the first episode, Funco is watching a young boy and girl at a shooting booth at the festival. The boy knocks down a prize, but the booth attendant claims he has to also knock down the stand in order to win the prize, which he conveniently forgot to mention. Funco then volunteers herself, and shoots both the prize and the stand, but now the attendant claims her shot didn't count because she's a pro attending the nearby school (after taking her money of course). Then the teacher shows up and fires, and although he has a good stance, his shots are terrible and he misses the prize, despite somehow being allowed multiple shots when the other characters were only allowed one.
Made of Iron: Almost literally: since the girls themselves are guns, they're made of metal, which means that they can take bullet hits better than a flesh and blood human could.
Although some guns are made of plastic/polymer. Apparently they are vulnerable to UV exposure.
Male Gaze: Quite evident in the closing credits. The clips of the battle rifles/high school girls include FAL with very short shorts, no bra and an open jacket that just barely covers her breasts, G3 getting fulled clothed but leaning down with a heavy focus on her ass, and most blatant of all, a nude Ichiyon with her private parts covered only by a strategically-placed rifle and boot.
Malevolent Masked Men: Some girls show up in episode 9 wearing masks, and then they start shooting up the secondary girls later in the episode.
More Dakka: Ichiyon switches to this in her duel with Ichiroku... and doesn't hit her at all.
Most assault rifles can fire on full auto, but as an M16A4, Ichiroku is limited to 3-round burst because full auto uses ammo too fast.
Battle rifles in general are known for their poor accuracy when fired in full auto, and the M14 is even worse in that regard because its lack of an inline stock exacerbates the high recoil inherent to full-auto fire with full-power ammo.
Motor Mouth: M10-chan, who proceeds to fire off an entire panel of text in about 10 seconds, causing FNC and Sig to wince in pain...until she runs out of ammo. Being of the Ingram MAC-10 family, she has a massive rate of fire.
Not So Different: After spending 2 episodes putting down L, 16 realises she's not so different after all, when she remembers the M16's troubled performance in Vietnam.
Power Copying: Sig learns G3's secret technique after observing it in their sniper duel.
Pragmatic Adaptation: While the anime keeps the Atami shootout from the manga, it differs in several aspects from the source material. Aside from the fact that the girls are actually fully-equipped with tactical jackets, Galil is taken out early, making it possible for Sako to step into her role, and the high schoolers (G3, FAL, and M14) intervene in the fighting as well. The biggest change of course is the appearance of the Soviet Major, who gives out the Break Them By Talking speech to Sensei and FNC in the manga; in the anime, AK-74 gives the speech instead.
Sacred First Kiss: Funco loses hers to Sako at the end of the Jungle Wargames arc. Funco's really upset as she was waiting until she had been registered.
The show does explain how the British military were eventually armed with the L85A2. Alongside the problems they encountered such as the frequent jamming, their issued magazines falling from the rifle and parts breaking down before the L85 has been modified to the A1 and A2 standards. Poor L-chan never got the modifications, though.
The evolution of the M16 series with the differences between the various M16 rifles. Also shown with Ichiroku constantly taking baths and cleaning herself excessively, as the M-16 tends to jam when not maintained properly.
The hand signals used by the assault rifle teams in the jungle wargame story.
Aspects of urban warfare were shown during the gunfights between the Seisho students against the AK faction, including suppressive fire to provide cover and crouching to avoid being an easy target by using the corner.
Shout Out: When the girls visit Enoshima, FNC notices (and is confused by) a shop selling Tari Tari goods.
Too Dumb to Live: "Sensei" for some strange reason brings up Funco's thong/skeleton stock. The result: he was hospitalized even longer. He does it again by accident in episode 7, although FNC at the end of the episode pouts (after getting suspended again) and says that she didn't hit him; rather he fell out of the window in his apartment on his own.
Transfer Student Uniforms: G3 and her MP5 sisters wear the uniforms of their old school. The exception is 53, which is apparently a reference to the fact that she is the only G3-based gun to appear in the series with a sliding stock.
Urban Warfare: The Red Steel High-based AK faction engaged all of the Seisho assault rifle girls, fighting throughout Atami with urban warfare tactics (sans military support and all). Ms. Fujiko and the battle rifle girls join in the fight, assisting the latter with a super friendly Galil. The AK faction receives help from 2 other AK derivatives, the Bizon SMG, and the Saiga-12 self-loading shotgun.
In the anime, Galil gets injured and Sako gets in the fun.
Ventriloquism: Sig does it in episode 9, which surprises everyone.
What the Hell, Hero?: Ichiroku/M16 constantly bashes Eru's performance and frequent breakdowns, which causes the latter to attempt skipping the jungle wargames tournament.
Who Is This Guy Again?: When Sensei sees Fujiko-sensei (the high school teacher) without her eyepatch and hair tied back, he's utterly confused as who she is at first.
Widget Series: Anime viewers who like moe will be put off by the guns, and gun fans will most likely be put off by the moe. Only those who can appreciate - or tolerate - both genres will be able to watch this show.
William Telling: A variation of this occurs in episode 9. Sig annoys HK by calling her Chuusuri-chan, and Chuusuri shoots the cover on the book Sig was reading on the beach named Wilhelm Tell, which featured an arrow piercing an apple on the cover. After getting it shot, Sig holds the book up, and points out that its a library book, and Chuusuri gets a scolding from one of the teachers.