The way things work between Egypt and Saudi Arabia is that Egypt is now expected to come to the aid of Saudi Arabia in case of an emergency.
I recently noted this deal. And note the French role as an alternate source of military hardware for Egypt which has been buying American since kicking out the Soviets more than three decades ago.
In a world of growing privatized military capabilities, this is at the high end when a nation buys another nation's military capabilities.
Once the Saudis did this with Pakistan, buying complete brigades to protect the kingdom.
Some might say the Saudis did this in 1990-1991 because we technically turned a profit on the Persian Gulf War after counting all the Gulf (and other) monetary contributions.
(But it wasn't really an example since it was in our interest to reverse the Iraqi conquest of Kuwait. But it did show how Saudi Arabia could purchase capabilities they don't have.)
It will be interesting (not in a good way, mind you) to see what circumstances could trigger the activation of this link.
UPDATE: Here's a circumstance:
The deputy commander of Iran's powerful Revolutionary Guard said Iranian forces will close the strategic Strait of Hormuz to the United States and its allies if they "threaten" the Islamic Republic, Iranian state media reported on Wednesday.
Ah, feel the power of the fully operational nuclear deal with Iran turning them into a responsible regional power and American partner!
Normally you'd figure we'd be the one to keep the strait open:
The U.S. and Iran have a long history of confrontations in the Persian Gulf. They even fought a one-day naval battle on April 18, 1988, after the near-sinking of the missile frigate USS Samuel B. Roberts by an Iranian mine. That day, U.S. forces attacked two Iranian oil rigs and sank or damaged six Iranian vessels.
A few months later, in July 1988, the USS Vincennes in the strait mistook an Iran Air flight heading to Dubai for an attacking fighter jet, shooting down the plane and killing all 290 people aboard.
But perhaps the Saudis are unsure of our commitment what with our advice that Saudi Arabia share the Persian Gulf with Iran.