A search of the Internet Digital Archive with "*Field Manual FM 17", then filtered for only publications prior to the mid 1950's, turns up a wealth of good information on the organization and deployment of US Armored Divisions from 1942. (Plus this unrelated 363 page Staff Officers' Field Manual (FM101-10) of Organization, Technical, and Logistical Data (1941)). Some of the most interesting in terms of this question are listed below.
Yes, U.S. tactical doctrine definitely promoted a tanks first attack philosophy, with repeated emphasis on speedy conversion from march order into combat order. Of the five example organizations for march and combat order, two specifically outline rapid deployment into a tanks first attack across a two Combat Command (~brigade) front. My reading of specifically FM 17-10 #48.g is that rapid swarming of the defense by light tanks, either with or without heavier support, was intended with the triple purpose of:
ascertaining opportunities for a coup du main;
locating and maneuvering towards the defenders flanks, simultaneously interfering with defenders' ability to ready; and
directing, and supporting, advance of the main striking echelon to the most advantageous point of attack.
Armored Force Field Manuals
Chapter 4 - Marches
16. General ... b. The Armored Division marches in one or more columns organized into combat commands. ....
20. Formations.- a. ... For each of these formations, three tactical groupings have been made within the division. Two of these groupings in each formation are combat commands. The third grouping remains under the direct orders of the division commander and may be regarded as a division reserve. ...
c. ... The essential purpose of the groupings is to form teams which habitually operate together, thus making possible intimate and uniform team training. This tactical grouping also simplifies orders and control. The tactical organizations as set up are suitable for and easily deployed into attack formations (A1-A2-A3-A4 and A7) which are show and explained later in the text. ...
f. Depending upon the formation adopted the infantry regiments may move in rear of the tank elements in advance of such elements or with these elements. ...
g. Normally, infantry and engineers will be attached to combat commands in order to render prompt assistance in crossing obstacles and in demolitions.
Of the five example attack formations described only one (A3) has infantry leading the assault unsupported by armour. Two formations (A1 and A2) appear to be designed for a meeting engagement, with infantry only in the third echelon and reserve, leading with the light tanks. The final two (A4 and A7) are light and heavy assaults with infantry in the lead echelon directly supported by various combinations of light and heavy tanks, artillery, and engineers.
The Combat Command organization of all five example attack formations exactly mirror a corresponding example march formation, and is intended to be deployed into, without undue delay, from that march organization.
19. Engineers.-a. The role of the engineers with armored force units, its characteristics, and tactical and technical employment are given in FM 5-5 and 100-5. ...
20. Infantry.-a. The role of the infantry with armored force units, its characteristics, and tactical and technical employment are given in FM 100-5. ...
48. General.-...g. Tactical groupings. In attack the combat command groups generally are disposed into four parts: a reconnaissance force (consisting of organic reconnaissance units and attack units), a striking force (the striking echelon consisting of tanks with engineers attached), a supporting force (consisting of the support echelon, i. e. the infantry, artillery, and tank destroyer units), and a reserve. Whether the striking force makes the initial attack or main attack will depend on the terrain and the extent and dispositions of the hostile antitank defenses.
Evolution of U.S. Armored Doctrine - Operations
FM 100-5: Tentative Field Service Regulations - Operations - October 1, 1939
No mention of independent armored units except in direct support of larger infantry/cavalry units. Pursuit and reconnaissance the domain of Cavalry (Mounted Infantry) Divisions.
FM 17 Armored Force Field Manual - Employment of Armored Units (1940?)
A compact, fully illustrated, guide to US Armored doctrine at the division level. Clearly inspired by events of September, 1939, if not also ay-June, 1940.
FM 100-5: Field Service Regulations - Operations - May 22, 1941
Adds more detailed and varied operational guidance for additional Special Operations: woods, towns, mountains, winter weather, jungle and desert. Outlines basic airborne and air transport missions. Adds detailed outline of the basic triangular Armored Division, along with tactical guidance on reconnaissance, security, marches, offense, and defense.
FM 17-10 Armored Force Field Manual - Tactics and Technique - March 7, 1942
More detailed recommendations on conduct of Armored Division reconnaissance, security, marches, offense, and defense operations.
FM 100-5: Field Service Regulations - Operations - June 15, 1944
The (nearly) fully developed U.S. tactical doctrine.