The fund was incepted in July 1973 and is managed by the Wellington Management Company. The fund's main objective is to seek a high and sustainable level of interest income. The fund invests in a widely diversified group of long-term bonds, most of them issued by corporations with strong credit ratings. It may also invest in U.S. Treasury securities and mortgage-backed securities. The fund, to achieve a high degree of stability in interest income, maintains an average maturity of between 15 and 25 years. Within that range, the average maturity may be adjusted to take advantage of expected changes in interest rates. The fund also seeks to improve returns or its income stream by emphasizing individual securities and sectors of the bond market that represent good value based upon historical yield relationships. Dividends are declared daily and distributed monthly. Capital gains, if any, are distributed annually in December.