In another sense, he was anything but alone.
There was the fraternity of other hikers on the trail. There was his wife Karen, back home in Tennessee, ordering supplies and providing moral support. There were the "trail angels," anonymous benefactors who do things like leave soft drinks or snacks on the trail for hikers. There was the diner waitress whose family took him in when he was injured.
"You can't make this thing without a lot of help from others," said Browning, who retired from Aerospace Testing Alliance, the primary contractor for Arnold Engineering Development Complex, on Feb. 29 and started hiking March 3.
Only about a quarter to a third of the 2,000 people who start hiking the 2,190-mile trail each year complete it. On July 19, after four months, two weeks, and two days, David Browning became one of them.
Browning, a lifelong hiker, had been on parts of the trail before, but this was his first time to attempt the entire route, an arduous treck along the ridgeline of the Appalachian Mountains.
"It's not a level trail, by any means," said Browning.
It starts in Georgia -- but you've got to hike an 8 1/2-mile "approach trail" from Amicalola Falls to the trail's official start on Springer Mountain. From there, it heads north, ending on Mount Katahdin, at Baxter State Park in Maine. The trail was first conceived in the 1920s and originally completed in 1937.
Various reroutes and improvements through the years have altered its official length. Nine out of ten walkers take the trail from south to north.
Heading the other direction requires starting much later, since Mount Katahdin doesn't open to hikers until June.
Browning carried a pack with a one-occupant tent, a sleeping bag, an inflatable mattress, a camp stove and cooking utensils. That equipment weighed about 25 pounds, before counting food or water.
The pack averaged about 32 pounds towards the beginning of the trip. In the Northeast, where potable water sources are harder to find on the trail, he ended up carrying up to 40 pounds.
Browning preferred to sleep in his tent. In case of inclement weather, there are three-sided shelters about every eight to 10 miles on the trail, and occasionally facilities like hostels. There are even some lodges along or near the route which offer special deals to hikers.
Most of those on the trail are in their 20s.
"People in their 30s and 40s have jobs," quipped Browning. He fell in with another hiker in his age range, a man from New York, and walked with him about 600 miles, but the New Yorker had to take a break and didn't finish the trail until August.
"There's bright sunny days," said Browning, "and there's also rainy days." Most of the rainy days were when Browning was passing through the Mid-Atlantic states.
"It rained quite a bit on me until I got to New Hampshire," he said. Near Lickdale, Pa., the trail was underwater for about 20 miles. He hitchhiked into town and was picked up by a 90-year-old man who had hiked the trail in 1980.
The White Mountains in New Hampshire had some of the prettiest scenery along the route, said Browning, but Mount Washington in that range has some of the most severe weather in the U.S., both in terms of low temperatures and wind speed.
There are historic sites along the trail as well. Harper's Ferry, W.Va., was the site of John Brown's famous raid and was a Confederate stronghold during the Civil War. There are stone fortifications parallel to the trail. The trail passes within 20 miles of Gettysburg and also near Antietam.
Browning passed through or near a town about every three to five days, he said, more often in New York and Connecticut. That's a good thing; "You don't want to carry more than about five days worth of supplies," he said.
In some places, like New York, hitchhiking is illegal, and it was much harder to find a way from the trail to the nearest supplies.
In one such place, Browning encountered three Hispanic families camping for the Memorial Day weekend. He was down to oatmeal and peanut butter, and when the families offered him a hamburger he gratefully accepted.
One of the men -- a native of Colombia, now a U.S. citizen -- drove him into Peekskill for supplies. The town had a Walmart, a far cry from the high prices and small selections with which Browning usually had to contend.
"It was like going to heaven," he said.
The man then took him to a laundromat, and even to a nearby river where Browning could submerge his air mattress and find a nagging leak so that it could be patched. He then returned him to the exact point on the trail where he'd left his journey.
In Maine, he had an accident.
"I banged up my leg pretty good," said Browning, who thinks he might actually have fractured his tibia. He called Karen and talked about coming home, but he was only 250 miles from the end of his journey and she told him not to give up.
A married waitress at the Little Red Hen Diner in Andover ended up taking him home, where her family -- she and her husband and one set of parents -- put him up for five days of rest, including a Fourth of July cookout. He got back on the trail after recuperating, and walked the last 250 miles without incident.
The last 100 miles of the trail is in the wilderness -- 40 miles of climbing followed by 60 miles alongside beautiful lakes.
At the end of the trail, at Mt. Katahdin, he found ... his hat, which he'd lost in Pennsylvania. Another hiker found it and carried it all the way to the end, figuring that whoever lost it was heading in the same direction.
Now that he's completed the Appalachian Trail, he'd like someday to hike along the Pacific Coast, or perhaps from France to Spain along the Pyrennes. But those trips are in the future. Right now, Browning is still recovering, and trying to catch up on chores at his property in Normandy.
"My toes are still numb," he said.
Somewhere, the trail angels are smiling.