The Three Lions will have both Aston Villa striker Ollie Watkins and Brentford's Ivan Toney available off the bench.
However, given Harry Kane is captain and the guaranteed starting striker, many questioned the decision.
Asked about the selection, Southgate told reporters: “In terms of attacking, we’ve scored more goals than any other generation other than Walter Winterbottom’s, so I think we have been attacking.
“The different profile of strikers is the reason for three. They all offer something different. We know Harry is the starting guy, but Ollie and Ivan have different attributes and different strengths that we might need at any given time in a game.
“I think the way the game is now — five changes for competitive games, the demands on squads across the season — the squad is going to be tremendously important. We’ve got different options, and we’ll use them.”
Southgate continued: “I think all forward players do, not just strikers: wingers. I think they recognise the calibre of the man ahead of them, but it is a different dynamic for them.
“At their clubs, they are the men everyone looks to, so you feel differently. They’re both very, very good players and they are here because we believe in them. At the moments that they’re needed, they will deliver. I do recognise that attacking players need to feel confident and that there is belief in them.”