Williams expressed frustration at its dip in reliability at the German Grand Prix, as its troublesome 2018 campaign continued.
Williams had put in a more competitive display at Hockenheim, aided by a revised front wing, which assisted Sergey Sirotkin in making it through to Q2.
But Sirotkin retired under the Safety Car due to an oil leak while Lance Stroll was pushed into the garage just a few laps later after a brake issue was detected on his FW41.
Williams had only once previously this year retired due to a mechanical failure, and it marked its first double retirement since the 2015 United States Grand Prix.
“It was a particularly tricky race with the rain and these are always a test of the race operations and the drivers' responses to rapidly changing conditions,” said technical chief Paddy Lowe.
“I think we called it pretty well and would have been in comparatively good positions and possibly in the points, but both the cars broke down for entirely different reasons.
“This is a particular blow as if there is one thing we have achieved this year it is being significantly more reliable than last year, with only one other car related retirement this year.
“Sergey had an oil fire due to an oil leak somewhere in the engine circuit, but we are still investigating this, and in Lance's case he had a failure in the rear brake circuit, losing all control of the rear brakes.
“In both cases it was clearly necessary to stop the car straightaway.”
Added Stroll: “At one stage we looked like we were in a pretty promising position, but then the rain started to come in.
“Looking at the results, [Brendon] Hartley scored a point and we were in front of him before we stopped for the inters and then obviously we had to retire with the brake failure.”
Williams is now 14 points behind Sauber at the foot of the Constructors' Championship.
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