Texas National Guard soldiers unload evacuees at Katy High School, 50 miles outside Houston, on Aug. 28. (Alex Horton/The Washington Post)

Katy, Tex. — Some Texas Army National Guard soldiers have been running search and rescue missions for two days, and for Alpha company, their live-saving efforts are already starting to blur together.

Sgt. Joseph Knell could not remember what time Monday he helped pull twin granddaughters to safety from a flooded house in Katy as their grandmother looked on. His fellow soldiers guessed about noon.

“They were very thankful,” Knell said.

Knell and the rest of Alpha company are from the 172nd Brigade Engineer Battalion, a unit among the thousands of Texas Guardsmen coalescing for search and rescue operations after Hurricane Harvey touched off historic floods on the Gulf Coast.

Texas Gov. Greg Abbott (R) activated the entire Texas National Guard on Monday — about 12,000 troops — to conduct search and rescue operations as the death toll reached 12, with more fatalities expected.

Flooding on the coast has transformed highways and roads into churning rivers often navigable only by boat, complicating recovery efforts as Guardsmen began operations.

Troops led by young sergeants and lieutenants are directly coordinating with civil authorities on the ground with relatively few cues from senior leaders, according to Col. Scott MacLeod, the commander of the 136th Maneuver Enhancement Brigade and head of a regional FEMA response force.

“They’re grabbing [evacuees] and they’re going,” MacLeod said in a classroom doubling as his command post in Katy High School, where the Guard set up an operations nerve center for Task Force Harvey about 50 miles west of Houston.

“Formal plans will come later. Right now, we just want to get down there and help out fellow Texans,” he said, adding that about 1,000 troops are operating in the Houston area as of Monday night.

From left: Sgt. John McNeely, Sgt. Jeremy Kempt, Pfc. Alex Vu, Pfc. Katherine Johnson and Sgt. Joseph Knell of the Texas Army National Guard. (Alex Horton/The Washington Post)

Alpha company’s convoy snaked about 50 miles to Katy from Brenham, their unit headquarters, and immediately ran out-and-back operations whenever a truck and a squad or two of soldiers were ready.

“We wait for the word, then we spin up and roll out” for missions in and around Houston, Sgt. Jeremy Kempt said.

Pfc. Alex Vu helped recover a state trooper whose squad car was submerged up to the hood with water, he said.  A separate group of 31 troopers boxed in by high water near the school was picked up by Alpha soldiers and transferred to higher ground in nine-foot-tall tactical vehicles that cruise through floodwater.

Many rescue incidents have come from civilians flagging down passing convoys.

“It’s hitchhiker style,” Kempt said.

Rescue efforts statewide have involved more than 450 vehicles and 16 aircraft from the Texas National Guard, the Pentagon said. The Coast Guard has deployed 39 helicopters and seven fixed-wing aircraft like the C-130 to deliver food and water to evacuees, and is supported by U.S. Army units, Air Force crews and aircraft and two Navy vessels.

Six helicopters from the Utah, Nebraska and North Carolina Army National Guards were headed to the area Monday. The Marine Corps Reserve readied rescue assets from Houston’s Ellington Field Tuesday morning, including Zodiac reconnaissance boats and UH-1 Iroquois helicopters, a Marine Corps official said.

A Texas Army National Guard soldier at Katy High School. (Alex Horton/The Washington Post)

MacLeod said strong winds has hindered the use of aircraft. Limited night operations are possible if civil authorities deem them safe, he said.

The high-water vehicles buzzed outside Katy High School into Monday evening as trucks emptied evacuees and supplies were unloaded by drenched soldiers. Some of the evacuees were children as young as 3 years old who were moved to an assisted living shelter, their names and the phone numbers of parents scrawled onto plastic underneath life vests.

One woman repeatedly pleaded with a soldier about the medication that she left behind and wanted him to pick up if he returned for others.

Five Alpha soldiers discussed surreal encounters while they sat in the school’s vast cafeteria, empty except for a few comrades poking at rations and unwinding between missions. They described one man who offered to help move evacuees as sparks shot out from the engine of his pickup truck. In another moment, civilians on jet skis cruised streets-turned-canals to knock on doors and find people trapped in houses.

Kempt said some of his part-time soldiers who have not yet been pressed into active duty have used their own trucks to pitch in with relief efforts.

“If they can help, they’re trying. It’s one big mass effort right now,” Kempt said. When asked if the five Alpha soldiers had family in Houston, all five raised their hand. They were all safe, the soldiers said.

Pfc. Katherine Johnson, the group’s medic, ventured they were averaging four to five hours of sleep a day so far, but she expected that to drop as operations continue. Maybe two hours, one soldier suggested.

“Maybe an hour and 45 minutes,” she responded.

Other missions late Monday evening sparked frustration from soldiers over deteriorating conditions. One group on a scouting mission to find launch points for rescue boats confronted high floods and were unable to continue further. Their reconnaissance mission became a rescue operation as they encountered civilians in need of assistance, said one soldier, who declined to be identified because he was not authorized to speak to the press.

“We’re going to be working through the night,” he said.