What aircraft had the first pilot-assisted controls? This question about regulations regarding hydraulic flight controls got me thinking about the history of hydraulic or pilot-assisted controls. As aircraft get larger the control surfaces must grow proportionally but it seems that the forces required to move those surfaces may grow at a non-proportional rate. That means at some point they had to switch from a pure cable/pulley system to an assisted system.

What is the first aircraft to use an electrical/mechanical/hydraulic system to assist the pilot with the control surfaces? I'm mostly interested in an answer from a commercial aircraft standpoint.
It was the Lockheed Constellation and the P-80, both introduced in 1943. The DC-3 had hydraulic flaps, but the Connie was the first to have hydraulic flight controls.


  The DC‐3 had wings flaps powered by hydraulics (1934). But it wasn’t until the early 1940s that hydraulics were used to power the primary flight control surfaces on the Lockheed Constellation and P‐80 (first US Jet Aircraft).


Source: A History of Aviation Actuation, Control and Fluid Power (PDF)

Also in 1943, the Lockheed P-38J-25-LO version of the WWII fighter aircraft was fitted with hydraulic boosted ailerons.

Source: Lockheed P-38J Lightning, Joe Baugher