— Joe Mackenzie
He is described as approching sixty in 2045.
Operation Prodigal Son
Around April 2040, Mac was in Richmond, Virginia for the launch of the Operation Prodigal Son, the first significant mission of the newly created USLONGCOM. He was standing in front of the stage with other Navy officers including Captain Maggie Kauffman and Nathan Boss, the Executive Officer, both of the USS Benjamin Franklin.
Four Waters City
Weeks after the send-off, the Franklin's crew found itself above Four Waters City, a settlement in the middle of the Corn Belt. The town organized a mass lunch for the entire dirigible's fifty-person crew. When walking along the main street guided by the mayor, Jacqueline Robinson, Maggie Kauffman sensed that the mayor was nervous. When asked about the reason of her nervousness, Mayor Robinson told Captain Kauffman about two crimes that were commited in the town.
A week before the Franklin's arrival, nine years old Angela Hartmann was given drugs by a man called Roderick Bacon and ended up in a coma. Her father found her in her bedroom, vomitting and beat Roderick to death.
Mac went to the Harmanns' house, examined the girl, reported to Maggie that little Angela might never be ok again and recommended that she'd be brought to a hospital on the Datum.
After that, Maggie passed a verdict about the case and told the town residents to report it to the Datum authorities, then had Mac treat Angela on the Benjamin Franklin before resuming their journey.
Around May, the Franklin was ordered to go to the Mine Belt to deal with an incident between humans and trolls in a stepwise Texas. Not far from the footprint of Houston, they found a rough camp where Maggie, Mac and Nathan met Sally Linsay, suspected to be a Long Earth vigilante.
Sally told them that three biologists tried to do cross-breeding experiments with trolls but since the trolls resisted and ran away, they shot them and left a cub orphaned. Sally managed to secure two of the scientists but let one go. The one that was allowed to escape called the authorities and this was how the Franklin ended up there.
Seeing that Maggie was among the less stupid twain Captain, the vigilante suggested that she could embark trolls on her ship and gave her a troll-call. After giving it some thought, Maggie asked Mac to find her some troll experts on the outernet.
It took him a couple of days searching on the outernet to come up him a number of universities who had studied trolls in the wild. This proved too dry to Maggie who preferred people who lived with trolls and didn't know them just as test subjects.
This is how she ended up in Madison West 5, at the Pagels' rescue center where they were using an extended family of trolls to help with the business. There she learned a lot about the trolls and, in the end, brought back a family of three trolls, named Jake, Marjorie and Carl by the Pagels, with her on the Franklin.
The march on Valhalla
In July 2040, Mac was among the senior Navy officers that were selected to take part in the military march on Valhalla, the symbolic stronghold of the rebellious colonies who declared their independance from the Datum government.
At the end of January 2045, they made a quick stop to Earth West 1,617,524 to pick up Snowy, who volunteered to be part of the expedition, Mac was among the party who went ashore and didn't showed much eagerness to go even if he worked here a few years before but never told Maggie about it and still didn't seem to want to talk about it.
As life aboard the ship kept on, it became obvious that there was some kind of tension between Mac and Snowy.
A bit further on their journey, around May 2045, as they were studying a sample of lifeform from Earth West 182,498,761, an Earth where two life from two different origins decided to cooperate, Maggie decided to settle the matter once and for all.
Beagles give birth to too many children, which causes them to regulally have devastating wars, in which many of them are killed. Every time they have a war, their progress as a civilisation gets reset.
Mac realised this, so he and some scientists tried to stop them having such large litters, by putting a chemical in the water supply. Unfortunately this plan backfired - the beagles realised that something had happened, and blamed one another, starting one of their wars.
Around the end of August 2045, when the Armstrong II and the Cernan took position over Happy Landings to deal with the threat posed by the Next, Mac was in Maggie's cabin when Ed Cutler brought, to their surprise, a briefcase containing the enabling mechanism of a nuclear weapon.
Since Maggie was the only one capable of giving the final order, Mac suggested to hold a hearing between two advocates, one for the use of the weapon and the other against. In the end, Mac was designed to argue for the pros and Joshua Valienté for the cons.
After a heated debate, in the end, Joshua prevailed and the nuke was disarmed. The Navy twains then left Happy Landings in peace.