A grand total of 1,155 players have represented the club in Football League action, but he’s the only one to have played in a World Cup while a Town player.
Having scored three times, including arguably his country’s most famous goal, in the 1982 World Cup in Spain, Armstrong got a second taste of the game’s biggest tournament in ‘86 in Mexico, thanks largely to his mutually-beneficial move to Chesterfield.
His time at Saltergate might have been fleeting, but it was highly significant for both parties.
“I needed games, basically,” said the 64-year-old, from his Majorca base.
“I had joined West Brom and Ron Saunders had taken over.
“He didn’t want anyone living more than 25 miles away and myself, Jimmy Nicholl, Imre Varadi and Garth Crooks were all outside that boundary.
“John Duncan phoned me with about 10 games to go.
“They were struggling at the bottom of the table.”
Duncan’s Spireites were fighting for their Division Three lives in the 1985/86 season and the Town boss spotted an opportunity to bring in a player he was certain could help.
“I knew him from the Spurs days and he was playing for Northern Ireland,” said the Scot.
“I knew what he could do, play up front or on the right.
“He wasn’t getting first team football at West Brom so it was dual benefit.
“I had a right sided midfielder who could score goals and he had the chance to get himself fit.”
The man who, four years earlier, had fired through the legs of Luis Arconada to give Northern Ireland a shock 1-0 win over World Cup hosts Spain did what Duncan hoped he would do and the move paid off in style.
“He did well, held down that position on the right, he was always a goal threat and supplied crosses,” said Duncan.
“He worked hard to get up and down.
“Gerry played regularly towards the end of the season and we stayed up.
“He came and gave us the impetus to go and have a good run and get his fitness.”
Playing just behind Armstrong on the right was a fresh faced 18-year-old.
Jamie Hewitt, who went on to play 506 league games for the club in two spells, says Armstrong was a great outlet for the team when they were under pressure.
He also credits the Ulsterman with helping him out in his first season of men’s football.
“Obviously he had a fantastic career and you sometimes worry as a young player when these stars come in, but he was brilliant with me,” said Hewitt.
“He helped me quite a lot, gave me a lot of good advice on how to play the game and obviously it was very helpful to the club.
“We were struggling down near the bottom of what is now League One and he contributed a lot to keeping us in the division, with his know-how and footballing ability.
“When we were under pressure we could give the ball to him, he very rarely gave it away.”
Another 85/86 season Spireite and fellow Northern Irishman recalls a ‘smashing bloke’ joining the club and boosting morale.
Sean O’Neill said: “He was obviously a good player.
“He just brought a bit of confidence into the side with his experience, his knowledge of the game.
“I think he steadied the ship a little bit.
“He was always available for the ball, calmed everything down and gave you a breather.
“I’ve got good memories of him, he was a big help.”
Armstrong was equally grateful for the chance to play games.
“We did very well, I can’t remember losing many games, we won and drew a lot and got enough points to stay up.
“I was training at Tottenham every day and went up for match days and it worked out very well.
“I got my games and went off to the World Cup.
“The last game of the season John didn’t want me getting injured before the World Cup and I remember sitting on the bench.”
That summer Northern Ireland were unable to repeat the heroics of ‘82.
“Spain was a great tournament for us, we played brilliantly, very, very well,” he said.
“I was very proud of the boys, we put 100 per cent into it.
“In ‘86 we were all older and altitude was a big problem for us, not the heat.
“We trained out there and we were out of breath after running for 10 or 15 minutes.
“That was a problem in games.
“I was 31, Pat was 32, some of the other lads were older.
“The team had aged and Billy (Bingham, Northern Ireland manager) knew he was having to replace a lot of us, and he did.”
Armstrong didn’t feature in the 1-1 draw with Algeria or the 2-1 defeat by Spain.
However the final group D game on 12th June, a 3-0 defeat by a Brazil side featuring the likes of Sócrates and Zico, gave Armstrong his final taste of international football.
He came off the bench on 71 minutes to replace David Campbell and carved out his own special place in Chesterfield history, before his time as a Spireite came to an end upon his return from Mexico.
“My last game for Northern Ireland, and Pat Jennings’, was against Brazil in 86, 32 years ago this week. I know the day because it was Pat’s birthday,” he said.
“Chesterfield offered me a contract and I wanted to sign but it wouldn’t have worked out.
“I was asked to go to Brighton and ended up signing for them.”
Armstrong’s international career amounted to 63 caps, 12 goals and six World Cup appearances.
Although he will undoubtedly be remembered by many for the ‘82 winner against Spain, he’s rightly proud of his other contributions in the tournament.
And opportunities to reminisce with the men who shared those special moments present themselves regularly.
“People only talk about that goal, they don’t talk about the one against Honduras or the one against France, they never talk about the other goals,” he said.
“The players, we keep in touch.
“I spoke to Jimmy Nicholl recently, I spoke to Pat Jennings yesterday, Mal Donaghy and Ian Stewart work for the FA and I see them, Billy Hamilton, John O’Neill does radio stuff and I see him at a lot of games.
“We had a great bunch of lads.”
Armstrong played 84 league games for Spurs, scored Watford’s first ever top-flight goal, spent two years with RCD Mallorca and graced a pair of World Cups.
But little old Chesterfield and the dozen games he played still rank among his fond footballing memories.
“I’ll always remember the Crooked Spire.
“And the lads were great.
“I loved coming up there for games.”