Basement trap under bathtub

Hi, when I get done replacing my old galvanized 2" waste pipe taking the kitchen sink water from the front of the house I want to replace this trap shown. Coming down from the bathtub above, when the bath was re done 10 years ago, they ran a flexible nipple from the drain into an 1 1/2", it looks like, galvanized nipple into the old trap. What is this trap, I see J traps, U traps around with cleanouts. I know I don't have to exactly duplicate this thing, (which dates to before WWII when the house was built) but I want a trap with a cleanout and enough room in it so accumulation won't block it easily. I want to at least know enough to know what to ask for at my local plumbing supply. I know I can just take this picture in but I don't like to look like a complete idiot. Thanks.

It is a version of a "drum trap". You should NOT need a cleanout in the trap, because most plumbers would snake through the tub's overflow opening, with water in the tub, so that the debris would be washed away after they dislodge it. Also, it is tiring snaking overhead and messy when the plug is removed. A "good" plumber could have that trap removed and replaced in a little over an hour.

Drum traps are no longer allowed here.

Normally when I see a drum trap, there is no vent in the branch drain. When the tub is replaced, the drain should be replaced with a common p-trap, and that trap will need a proper vent.

Thank you both

I am not sure where you are, but EVERYWHERE I have been, when they used drum traps, they ALWAYS had a vent, just as if they used a "P" trap. There is NOTHING unique about a drum trap what would allow them to eliminate the vent.

Thanks. This was installed in the late 30's. The 1 1/2" galvanized coming out of that trap runs 5' into the 4" cast iron soil stack, via a wye on the cast, which rises right up to the roof. The only other vent in the house is for the kitchen sink which at the opposite end of the house. This drum trap under the tub/shower has been working fine since the home was built except of course all this galvanized has exceeded its lifespan and has narrowed. I was going to put a 2" P trap under here and run inch and a half to where the old one goes. I guess i could use 2". Just out of curiosity, if someone wanted to comply with current code, how would you vent into the old cast iron going to the roof? Here is a view of the galvanized from the shower going into the cast iron. You can see the wye painted white in the middle of the photo