Take that Fidelity. 

After a salvo from that rival this past summer, Vanguard on Monday said it would drop the investment minimums for its low-cost Admiral Shares effective immediately, to $3,000 for 38 index funds. That's down from the previous minimum investment of $10,000.

If the new structure had been in place for the 12 months ended Oct. 31, investors would have paid in aggregate $71 million less in fees, Vanguard estimated.

Vanguard chief executive Mortimer "Tim" Buckley said in a statement: "Our unique, client-owned structure enables us to consistently pass along economies of scale and lower the cost of investing for our clients, so they keep more of their returns."

The lowered minimums represent expense savings of 15 percent to 71 percent over the Investor share class, depending on the fund.

Fidelity last August  launched two mutual funds with no fees — yup, zero.

Fidelity Zero Total Market Index Fund and Fidelity Zero International Index Fund are available with no fees to individual retail investors who purchase shares through a Fidelity brokerage account. The Boston investment giant also slashed fees on some index-based stock and bond funds.

Among Vanguard's 38 funds with lower minimums are the industry's two largest equity index funds (the $707.6 billion Vanguard Total Stock Market Index Fund and the $431.2 billion Vanguard 500 Index Fund); and the industry's largest bond index fund (the $199 billion Vanguard Total Bond Market Index Fund).

Vanguard also filed with the Securities and Exchange Commission to launch lower-cost Admiral shares of five additional index funds: Vanguard FTSE Social Index Fund, Vanguard FTSE All-World ex-US Small Cap Index Fund, Vanguard High Dividend Yield Index Fund, Vanguard Long-Term Bond Index Fund, and Vanguard Total World Stock Index Fund. The new shares are expected to be available in the first quarter of 2019.

Vanguard introduced Admiral class shares in November 2000 to offer cost savings to large and long-tenured accounts.

The fee wars among Fidelity, Charles Schwab, online brokers, and robo-advisors seeking lower-minimum accounts rage on, as they seek to mimic Vanguard's low-fee model. As other firms drop fees toward Vanguard's levels, meanwhile, Vanguard global assets under management have grown to more than $5.3 trillion.

Its firm-wide average expense ratio now totals "an all-time low of 0.11 percent — one-fifth the industry average," the Malvern-based investment giant said in its press release. That compares to what Vanguard said was the industry average mutual fund and ETF expense ratio of 0.62 percent as of Dec. 31, 2017. Industry averages exclude Vanguard.

Vanguard recently added to its line-up of 80 U.S. ETFs, with two new environmental, social, and governance ETFs. In February 2018, the firm also broadened its line-up by introducing its first actively managed factor ETFs.

Admiral Shares of Vanguard's actively managed stock and bond funds will still require at least $50,000. Any remaining Investor class shareholders will be automatically converted to Admiral Shares beginning in the second quarter of 2019. Share conversions within the same fund are tax-free, Vanguard announced.