Back in the day, Liverpool Corporation routes to Pier Head mostly ended with either C or D [there were exceptions], C meant Pier Head via Church Street, D meant Pier Head via Dale Street.
Then all after sorts of road changes, with one way systems, & pedestrianization schemes, meant by the early 80s, C routes to Pier Head went via Hood Street Gyrotory, & Lord Street, the D routes to pier Head went via Churchill Way Flyovers, then inbound via Dale Street, outbound via Tithebarn Street
You learn something new every day, I never knew what the letters stood for. I can remember going over the flyover and dropping onto Dale Street on the bus and getting off near central.
I used to hate getting the 15D as it went to Kirkby town centre, round Northwood, through Southdene, then onto the Lancs, it always swapped drivers at Gillmoss, then went through Norris Green, Breck Raod and into town, took forever. The other bus was the 15C and that went through Westvale, then Fazackerley/Walton/Scotty into town. I used to get that to the match, get off on County Rd, pop in to see my Nan, then walk through Stanley PArk - happy memories