The 76 workers were packed and ready Thursday night for final meetings and their Friday morning departure but still a little worried about what lies ahead and what they're leaving behind.
For Marcus Forrest, that's a wife and three sons. They understand, even his youngest.
"He goes, 'I guess you're going to turn people's power on, dad,'" Forrest said. "They kind of know that comes along with the territory. That's what we do. The phone rings, you answer the phone, and you go. He always says, 'If my lights were out, I'd want you to come put them back on too, dad.'"
Then there's work and devastation the likes of which even the most seasoned Ameren worker has never encountered: different terrain, climate, rigging systems. They'll focus on rebuilding that final mile of infrastructure from transmission lines to the homes and businesses.
More than 130 days after Maria, nearly a half-million people (more than 30 percent of customers) still do not have power in Puerto Rico.
Ameren shipped supplies, including 25 trucks earlier this month. They were delayed in stormy seas but will be waiting for this group along with 12 to 14-hour days, 7 days-a-week.
Co-workers in St. Louis not making the trip signed a banner wishing the group "buenas suertes" (meaning "good luck"). They'll need it.
"We're going to work three weeks at a time, then rotate people because they're working seven days a week for three straight weeks," said Mark Birk, Senior Vice-President for Ameren Missouri. "Then (we'll be) working to bring another 70 people down and we'll work on it as long as we need to, to get the island restored."
"We don't have just 76 people going," said Ron Pate, Senior Vice-President for Ameren Illinois.
"We have 9,000 people going, the support and stuff we have behind them. They'll get daily updates. I'm sure there will be some pictures that come back. We're able to share. Those 76 workers have the support of the other 9000 for sure."
"To go down there and see the look on people's face whenever you throw the switch and their power comes on there's nothing better in the whole world to hear the clapping, the smiles and 'thank you's'," said Brian Doran of Ameren Illinois.