Breakthru was part of the line of 3M bookcase games from the 1960s. copyrighted 1965, although it's a development and refinement of the classic "Hunt" games such as Fox & Geese and "Sixteen Soldiers" that date back to at least the Thirteenth Century. The game features a vague "naval" theme in the box art and game piece naming convention (a "flagship" and "destroyers") but it's really a pure abstract game.
One thing worth remarking about is the outstanding durability of the 3M packaging. The 3M bookshelf box may very well be the best game packaging ever, although some of the new euro-games also have very nice, attractive and sturdy boxes. Still, my copies of the seven 3M titles in my collection are all still in very good shape despite being more than 40 years old. Even the similar Avalon Hill bookcase games show considerably more wear and damage and no other games boxes from anywhere near that age can compare to the 3M boxes. The 3M games were marketed as premium games and live up to it.
Inside the box is a black plastic white-gridded 11x11 board. The Center square is marked with a circle surrounded by a 5x5 zone of squares. This is the setup zone for the "gold" fleet, which comprises a tall brass "flagship" and a dozen smaller "destroyer escorts. The Flagship must set up on the circle, while the escorts can set up anywhere inside the 5x5 zone.
The twenty metal "silver" destroyers can set up anywhere outside gold's setup area. The zones have no effect on play after setup. While no particular formation is required for either side, several suggested setups are provided in the rules, which are simple enough to print on the inside of the game box -- a very common place to find the rules for games of that era.
The rules themselves are exceeding simple. The players alternate turns, with Gold deciding who starts. In a player's turn he can either perform a "motion move" or a "capture move." A motion move consists of moving the flagship or two destroyers. Pieces can move any distance is a straight horizontal or vertical line, but not diagonally. A capture move, in contrast, consists of moving one piece diagonally one space into an enemy-occupied square and making a replacement capture, similar to a chess pawn.
The game ends when the flagship is captured or it escapes to a board edge.
Game play is tense, as both sides maneuver to hem in the other side and threaten captures. One blunder and the game can come to a quick end.
Abstract games don't appeal to everyone, but Breakthru provides a challenging play experience while not being quite as intimidating as chess. I think it makes a good game to play with kids because it makes them don their thinking caps while not being overwhelming. There are only two kinds of pieces and they all move the same way. There are no special or odd rules and the game plays quickly enough that most sessions can involve multiple plays. Some of the older Fox & Geese-type games have balance issues with optimum play, but Breakthru gives both sides a shot at winning.