VANGUARD MORTGAGE-BACKED SEC

The fund employs an indexing investment approach designed to track the performance of the Bloomberg U.S. MBS Float Adjusted Index. This index covers U.S. agency mortgage-backed pass-through securities issued by the GNMA, the FNMA, and the FHLMC. To be included in the index, pool aggregates must have at least $1 billion currently outstanding and a weighted average maturity of at least 1 year. All of the fund's investments will be selected through the sampling process, and at least 80% of the fund's assets will be invested in bonds included in the index.