Dawn Raid

What Does Dawn Raid Mean?
The action of a firm or investor buying a substantial amount of shares in a company (making it a target firm) first thing in the morning when the stock markets open. This is done by a stock broker acting on behalf of a company. Because the bidding company builds a substantial stake in its target at the prevailing stock market price, the takeover costs are likely to be significantly lower than they would be had the acquiring company first made a formal takeover bid.

Investopedia explains Dawn Raid
Like the dawn raid in war, the corporate dawn raid is done early in the morning, so by the time the target realizes it's being attacked, it's too late - the investor has already scooped up some controlling interest. However, only a maximum of 15% of a firm's shares can be bought this way. So, after a successful dawn raid, the raiding firm is likely to make a takeover bid to acquire the rest of the target company.