Does a fighter's Action Surge trigger Extra Attack?

Question

Context

A player in my game will play a fighter with a greatsword. At 5th level he has Extra Attack and the option to use Action Surge. PHB p.72 states:

Action Surge. Starting at 2nd level, you can push yourself beyond your normal limits for a moment. On your turn, you can take one additional action on top of your regular action and a possible bonus action.

Once you use this feature, you must finish a short or long rest before you can use it again. Starting at 17th level, you can use it twice before a rest, but only once on the same turn.

Extra Attack. Beginning at 5th level, you can attack twice, instead of once, whenever you take the Attack action on your turn.

The number of attacks increases to three when you reach 11th level in this class and to four when you reach 20th level in this class.

Confusion

The questions and answers that I find on here deal with multi-classing or Two Weapon fighting specifically, which don't really give a clear yes or no on my question.

The way I read these two features is that when a fighter takes an Attack action, he gets the Extra Attack. After using Action Surge he gets the opportunity to take another Attack action, and with that another Extra Attack. This results in four attacks with the greatsword in one turn, which sounds amazing but also rather powerful. Is this correct, or am I missing something?

Answer 1

Yes, a fighter gets their extra attack when using action surge

Action surge gives you an extra action on your turn:

On your turn, you can take one additional action on top of your regular action and a possible bonus action.

There is no restriction on what this action can be used for. Using it to take the Attack action would indeed then trigger Extra Attack since that feature triggers:

whenever you take the Attack action on your turn.

Is it powerful? Of course. But this is what fighter are good at: swinging weapons many times for high damage.

Answer 2

Yes, Extra Attack triggers on an Action Surge

At 5th level, a fighter may use Action Surge to gain an additional action. If they choose to use their action to take the Attack action, this triggers their Extra Attack ability.

While this is a good combination, it is important to remember that they can do this at that level once per short rest. It is a good blast of damage, but it's not sustained.

At 5th level your standard full-caster will gain access to 3rd-level spells. A popular 3rd-level evocation spell is Fireball, which deals 8d6 fire damage on multiple enemies. By comparison, with action surge your fighter deals 8d6 (plus 4x bonuses) slashing damage with a Greatsword, on one enemy, assuming he hits on every attack.

It is a powerful combination, but well-balanced; don't be afraid to let your fighter go crazy.

Answer 3

Yes it would

Extra Attack says that you can take an extra attack if you take the Attack action. This means that if you took the Attack action after you used your Action Surge to get an extra action, you would get the benefit of your extra attack since you are using your action to attack.

Answer 4

To answer your other question

am I missing something?

You might be. This feature is crucial for fighters to scale up with the rest of your players. It might seem powerful, but remember it's really only as powerful as the weapon they hold. Each class progresses differently, and for what fighters lack in general versatility they make up for in dealing damage. (Not to say fighters are useless outside of combat, but combat is where their focus is for sure.)