Josh Flint and Eoin Teggart were handed their Blues bows in the Leasing.com Trophy clash at Fratton Park.
Flint, who hails from Waterlooville, scored and recorded an assist on his maiden appearance while Northern Irish winger Teggart delivered a man-of-the-match display.
It was a comfortable success for Kenny Jackett’s side, with Ellis Harrison also firing a double.
And although Gallen was disappointed Pompey didn’t register a clean sheet, he felt it was a comfortable afternoon.
And the assistant boss was highly encouraged by Teggart and Flint’s displays.
Gallen said: ‘I thought it was pretty comfortable in the end.
‘We were disappointed that Norwich scored, I thought we were going to keep a clean sheet but it didn’t quite happen.
‘But overall it was pretty comfortable. We took the lead early on and it didn't look like Norwich were going to come back into it.
‘I think one of their wide players had two shots around the edge of the box that went wide. Other than that we were never in too much danger and player very well over all.
‘Josh Flint was making his debut and scored in the number-10 role. He had a good game and is a nice footballer.
‘Eoin played really well on the left-hand side. Not only did he put in some excellent crosses but showed a clean pair of heels, a lot of acceleration, a lot of pace and put in some excellent deliveries.’