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Ultraviolet (UV) observations of Type Ia supernovae (SNe Ia) are useful toolsfor understanding progenitor systems and explosion physics. In particular, UVspectra of SNe Ia, which probe the outermost layers, are strongly affected bythe progenitor metallicity. In this work, we present 120 Neil Gehrels SwiftObservatory UV spectra of 39 nearby SNe Ia. This sample is the largest UV(lambda < 2900 A) spectroscopic sample of SNe Ia to date, doubling the numberof UV spectra and tripling the number of SNe with UV spectra. The sample spansnearly the full range of SN Ia light-curve shapes (delta m(B) ~ 0.6-1.8 mag).The fast turnaround of Swift allows us to obtain UV spectra at very earlytimes, with 13 out of 39 SNe having their first spectra observed >~ 1 weekbefore peak brightness and the earliest epoch being 16.5 days before peakbrightness. The slitless design of the Swift UV grism complicates the datareduction, which requires separating SN light from underlying host-galaxy lightand occasional overlapping stellar light. We present a new data-reductionprocedure to mitigate these issues, producing spectra that are significantlyimproved over those of standard methods. For a subset of the spectra we havenearly simultaneous Hubble Space Telescope UV spectra; the Swift spectra areconsistent with these comparison data.

Swift UVOT Grism Observations of Nearby Type Ia Supernovae - I. Observations and Data Reduction