Vector Acquisition Corporation, the SPAC that merged with Rocket Lab USA in 2021 to form RKLB, had its sponsor, Vector Acquisition Partners, L.P. (controlled by Vector Capital Partners V, Ltd.), file this initial SC 13G on Feb 16, 2021, reporting beneficial ownership of 7,950,000 Class B ordinary shares as of Dec 31, 2020. These 'founder shares' represent 19.9% of total shares outstanding (based on 40M total shares per recent 10-Q) and are automatically convertible on a 1:1 basis into Class A shares at the initial business combination, subject to adjustment. Filed under Rule 13d-1(d) for passive holders, it confirms standard SPAC structure with sponsor alignment via significant equity stake. No voting/dispositive power shared beyond sponsor control; general partner disclaims beneficial ownership beyond pecuniary interest.

For Rocket Lab investors, this historical filing confirms the SPAC sponsor's substantial 19.9% pre-merger stake, signaling alignment with the deal's success via founder shares. Post-merger (completed April 2021), these shares became part of RKLB's float after lockup expiration, but no immediate dilution or selling indicated here. Monitor future 13D/G amendments for sponsor sales, which could pressure stock if significant.