http://www.retrogame-labo.com/ss/game007.html
TOOK long enough to ferret these out...Let's see if I can decipher what the Bing translator has to say...
1. Caveman-class submarine "Argos" (...And how did Bing think the katakana for "Caveman" signified "Which"?!)
2. SICBM control units "Trumpet Lilies" (For those of you not familiar with it--like me--SICBM means "Small InterContinental Ballistic Missile.)
3. Automated machine master device "Manriki" (Yes, Manriki is in katakana. It can mean "vise" or "capstan".)
4. Stone Palace three-headed monstrosity "J3" (As in J-cubed. "Three-headed monstrosity" was the best way I could think of to understand 邪悪の３条 after getting the kanji definitions. I'm not even remotely fluent in Japanese.)
5. Sentinel sub-human "Sougon" (荘厳; After looking in Wiktionary, the best I can come up with for a meaning is "Steadfast"...I'm not sure whether the sub in sub-human is meant to mean "beneath" or be short for "submarine")
6. Humanity-cleansing system "Yugusukyuure" (Unfortunately, Yugusukyuure is in katakana, and no kanji are supplied, so I have no idea what it's supposed to mean. Sounds like Destroy And Satsujin wanted to have Earth all to themselves...)
EDIT: Bah, I was too hasty in reading the first name, and mistook the last kana for "su". It's actually a-a-go-(tsu)-ku, but I have no idea what Irem was going for.
EDIT THE SECOND: ...And I'm feeling a bit foolish because these were found out already: http://shmups.system11.org/viewtopic.php?p=238117. Well, not the purpose descriptors. Turns out the first boss is called "Argock".