The 19-year-old was serving in the RAF and stationed in Scarborough during the war.
Like so many thousands of men and women of the time, Sgt McConnell wrote home to his partner in Lanarkshire, Scotland, as a way of getting through his darkest days.
"Oh darling, I'm so lonely without you," he wrote to the unnamed partner in one.
Now, 80 years on, the letters between the two have been unearthed from beneath the floorboards of Scarborough's Esplanade Hotel while it carries out renovations.
The correspondence was among a treasure trove of relics from the war, including ticket stubs, handwritten poems, cigarette packets and chocolate bar wrappers, and is now in the safekeeping of the Scarborough Archaeological and Historical Society.
Scarborough had been a hub for the RAF during WW2, with the Esplanade requisitioned by the Army.
"We got a message through from the hotel to say they had found all this material," says Marie Woods, from the Society.
"They wanted to know what to do with it all. I wasn't prepared for the pictures they sent through."
All the material was picked up by Ms Woods who brought it home and began to go through it.
"It was so exciting going through it not knowing what I would find," she said.
"These letters to one another were both there. Sgt McConnell has written in pencil as he ran out of ink, and he writes of planning to go to a shop to get more. So it is likely he sent the version written in pen and kept the pencil copy. To find a full set of correspondence is very rare, so naturally we were very excited."
After posting copies of the letters on their Facebook page, the Society received an email from someone who was able to shed a little light on the writers.
Heartbreakingly, Sgt McConnell was killed on Christmas Eve of 1943, when an Avro Lancaster III aircraft he was flying in alongside six aircrew collided mid-air with another Lancaster just north of Louth, near Grimsby. He was just 19 at the time.
Records show he was buried at Airbles Cemetery in his hometown of Motherwell.
Other letters discovered among the array of items included an account from a soldier named Jay Lancaster who wrote how the idea of dropping "empty bombs" was more appealing to him than "trying to stick a bayonet into someone".
"It really helps you to put yourself into their shows," Ms Woods added.
"It must have been unthinkable and the idea of dropping bombs and not knowing all the people you were killing would have been easier to cope with than killing someone upfront. So for me that was the most heart-wrenching thing to find."
The Society is now keen to see the letters reunited with its rightful owners, and are appealing for any descendants of either Sgt McConnell or his lover - whose name is given only by the letter 'M' - to come forward.
"It would be wonderful if we could track someone down," said Ms Woods.