It's a WW2 series set in Burma, starring a terrifyingly evil bastard and written by John "Judge Dredd" Wagner. It was pushing the envelope even for the 1970s. Wagner himself has expressed surprise that he didn't get censored, although he most certainly did in later reprints. You couldn't write this today. What I read was the 2011 Titan graphic collection, which is uncensored but still careful to make sure it doesn't get in trouble:
"This book is a work of fiction. Characters may have views and use language which some of today's readers may find offensive. The publisher and copyright holder in no way endorse the views expressed or language used."
In other words, soldiers use racist language while sticking knives in Japanese soldiers. Jap, nip, slanty-eyed and rice boys are all said regularly. "That Matumotu was one nip who sure deserved a little killin'!" (Darkie isn't black, though, and the only ethnicities here are British and east Asian.) This is all part of what makes the strip shocking. Joe Darkie is a monster who'll kill his own soldiers, torture captives and murder foes who are trying to surrender. "But that Jap officer nearly put the kibosh on the whole thing. Remember, a dead Jap can't cause trouble... so don't take prisoners - take scalps!"
What's more, it's often based on actual events. Wagner researched the Burma campaign in detail. Darkie being nailed to a roof? Meeker's arm getting amputation with a hunting knife? An ally being crucified and left to die in the jungle? The hate-fuelled racism? All real. The desperation and savagery? Yup, that too.
For what it's worth, the offensive language didn't bother me. Tomoko also had no problem with a WW2 comic about lots of Japanese soldiers getting killed with ultra-violence. However it's clear that Wagner didn't have anyone Japanese advising him. (I don't object there either, but it's noticeable.) None of the snippets of supposed Japanese dialogue that we hear made any sense to either Tomoko or me, with the oddest example being "shiva". The language has no native "V" sound. The Japanese names are also a bit off, e.g. Matumotu (instead of Matsumoto), Hamusa (instead of Hamasa), Hamuda, etc. The "Tokyo Rose" broadcasters never actually called themselves "Tokyo Rose", etc.
There are other ways in which it's challenging for a modern reader. As was common with 1970s UK war weekly comics, it's a repetitive, mostly plotless series of three-page episodes. (Occasionally you'd get a four-page episode, but those are rare.) Each page is big and jam-packed. It wouldn't be unusual to see a fifteen-panel page, so each micro-episode actually has as much story as a normal comic strip episode from 2000 AD or DWM today, or even a lot of 23-page US format comics.
Because of this, you can't take in at an entire page at once. It's too dense. You've got to shrink your focus and move along bit by bit, or else it's unreadable. Reading the whole thing is a little exhausting, especially since it wasn't meant to be collected and that's not its ideal format. It's meant to be a weekly three-page gut punch. The strip more or less stands up to marathoning, though, thanks to the glowering anti-heroism of Joe Darkie and the way he keeps burning his bridges and losing his soldiers. There's a definite progression. The number of survivors left in Darkie's Mob makes for a grim countdown to the end.
This series is so extreme that it's hard to appreciate it properly without reading some of the other, supposedly similar strips of the time. Today, you read it on its own and you just don't realise. However looking at stuff like Major Eazy, Johnny Red, etc. will make you realise how much more gruesome and extreme this is. It's full of memorable content, which in fairness includes a bit of characterisation. Wagner will sometimes choose to bring a supporting character alive for the reader. Joe Darkie himself, though, is on another level. He's a colossus. He towers above the stiff, abbreviated three-page format. He's one of John Wagner's ultimate bastard protagonists, transcending even Judge Dredd with his savagery, his dark, surprising backstory and a truckload of hatred.
He's a beast of the jungle. He's abandoned civilisation. He's a monster with a hunting knife, killing everything in his path unless you're an Allied soldier (and even then you're far from safe). Welcome to Joe Darkie's suicide mission.
"Men, one of you has to do without. There's no other way. I've got five long straws here, and one short one." (Two panels later, they're burying Mr Unlucky... and Darkie isn't even the biggest bastard in that episode.)