Hier die Erklärung:
Und hier das Ganze noch verständlicher:
Destroyers
Tier II - IFHE is not needed.
Tier III - IFHE is not needed.
Tier IV - IFHE is not needed.
Tier V - IFHE is not needed when top tier, but is useful when facing higher tiered opponents.
Tier VI - Generally speaking, IFHE is effective for all gun calibers, but of less value when facing tier VIII opponents. 120mm guns are especially taxed when bottom tier.
Tier VII - Generally speaking, IFHE is effective for all gun calibers, but of less value when facing tier VIII & IX opponents. 120mm guns are especially taxed when bottom tier.
Tier VIII
Japanese 100mm - Take IFHE
120mm - Not recommended
127mm - Effective when top tier. IFHE's use falls off dramatically against tier VIII+ cruisers and battleships.
128mm - Effective when top tier. IFHE's use falls off dramatically against tier VIII+ cruisers and battleships.
130mm & 139mm - IFHE Is reasonably effective due to ability to penetrate all tier VI & VII battleships and cruisers from tiers VI through IX.
150mm - IFHE Is reasonably effective due to ability to penetrate all tier VI & VII battleships and cruisers from tiers VI through IX.
Tier IX
Japanese 100mm - Take IFHE
113mm - Not recommended
120mm - Not recommended
127mm - Not recommended
128mm - Not recommended
130mm & 139mm - IFHE Is reasonably effective due to ability to penetrate all tier VII battleships and cruisers from tiers VII through IX, but take it or leave it.
Tier X
Japanese 100mm - Take IFHE
113mm - Not recommended.
120mm - Not recommended
127mm - Not recommended
128mm - Not recommended
130mm - Not recommended
139mm - Not recommended
Cruisers:
Tier I - Stop it, you twink.
Tier II - IFHE is not needed.
Tier III - IFHE is not needed.
Tier IV - IFHE is not needed.
Tier V - When top tier, IFHE isn't necessary, but it becomes very important against higher tiered opponents. Don't take it if you're German.
Tier VI
150mm - Not needed due to increased penetration of Nurnberg & Makarov.
152mm - Take IFHE. Reduced effectiveness against tier VIII+ battleships.
180mm - Take IFHE.
203mm - Don't take IFHE on 203mm armed ships.
283mm - Put IFHE down, Spee.
Tier VII
127mm - Effective when top tier. IFHE's use falls off dramatically against tier VIII+ cruisers and battleships.
152mm - Take IFHE. Reduced effectiveness against tier VIII+ battleships.
203mm - Stop it. Get some help.
210mm - Yorck is German. What are you doing? You don't need IFHE.
Tier VIII
152mm - Take IFHE.
155mm - Take IFHE. Mogami 155mm is one of the biggest winners with the IFHE rework.
203mm - I am going to hurt you.
Tier IX
152mm - Take IFHE
180mm - Take IFHE.
203mm - ...
305mm - Now you're just being silly.
310mm - Shut up, boobie-lady.
Tier X
127mm - Not recommended
130mm - Not recommended - Except SMolensk there you should take IFHE
152mm - Take IFHE
203mm - Where did I leave my chain-axe?
220mm - Not recommended
234mm - Not recommended
240mm - Not recommended
305mm - Nope.
310mm - Also nope.
Battleships Secondaries:
Secondaries only really get good enough to spec into from tier VII+ so we'll start there.
Tier VII
Nagato - Nope
Ashitaka - Nope
Colorado - Very no.
Sinop - Nope
Poltava - Shame on you, no.
Gneisenau - Nope, her HE pen is good enough without it.
Scharnhorst - If you want to be twinky and have her 105mm penetrate battleship extremities for the memes, go for it. But this is more of a joke than actually needed.
King Georgge V - Nope
Hood - Nope
Nelson - Nope
Duke of York - Nope
Lyon - Very no.
Tier VIII
Amagi - Nope
Kii - Her 100mm look SOOOO good, but their range sucks monkey butts, so they're not worth spec'ing into. Nope.
North Carolina - Nope
Alabama - Nope
Massachusetts - It's only effective when she's top tier. Otherwise, the use for this falls off dramatically. It's no longer really good.
Vladivostok - God no.
Lenin - Leave these neckbeard secondaries out of it.
Bismarck - Again, the 105s could use it but you don't NEED it. Use those skill points elsewhere.
Tirpitz - As per her famous big sister.
Monarch - HAHAHA, very no.
Vanguard - Also no.
Richelieu - Nope.
Gascogne - MAYBE if you brawl often with Gascogne. Actually, it would be fascinating to meet someone who simply plays Gascogne often. Nope otherwise.
Roma - Nope.
Tier IX
Izumo - God, no.
Musashi - HA! No.
Iowa - Nope.
Missouri - Nope
Georgia - Pass here too. You're just not facing enough lower-tiered ships where her penetration threshold works. Like the German ships, you can go for it if you want to giggle a bit, but it's not worthwhile.
Sovetsky Soyuz - Nope
Friedrich der Große - As before with other German BBs. It's only fun for the memes, but it's not needed. They're good without it.
Lion - Very no on toast.
Alsace - Nope.
Jean Bart - Nope.
Bajie - Nope.
Tier X
Yamato - No.
Montana - Also no.
Ohio - Also also no.
Kremlin - Also also also no.
Großer Kurfurst - Also also also also no.
Conqueror - Also also also also also no.
Thunderer - Also also also also also also no.
Republique - Also also also also also also also no.
Bourgogne - Say it with me: Also also also also also also also also no.
I suppose I could have just "TL-DR" - if German with 105mm at tier VII+, sure, otherwise Also No."